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Anthony J Baines

Publications and source records attributed to Anthony J Baines.

At least 19 recordsLinked to original sources
PubMed2006

Thermal stabilities of brain spectrin and the constituent repeats of subunits.

The different genes that encode mammalian spectrins give rise to proteins differing in their apparent stiffness. To explore this, we have compared the thermal stabilities of the structural repeats of brain spectrin subunits (alphaII and betaII) with those of erythrocyte spectrin (alphaI and betaI). The unfolding transition midpoints (T(m)) of the 36 alphaII- and betaII-spectrin repeats extend between 24 and 82 degrees C, with an average higher by some 10 degrees C than that of the alphaI- and betaI-spectrin repeats. This difference is reflected in the T(m) values of the intact brain and erythrocyte spectrins. Two of three tandem-repeat constructs from brain spectrin exhibited strong cooperative coupling, with elevation of the T(m) of the less stable partner corresponding to coupling free energies of approximately -4.4 and -3.5 kcal/mol. The third tandem-repeat construct, by contrast, exhibited negligible cooperativity. Tandem-repeat mutants, in which a part of the "linker" helix that connects the two domains was replaced with a corresponding helical segment from erythroid spectrin, showed only minor perturbation of the thermal melting profiles, without breakdown of cooperativity. Thus, the linker regions, which tolerate few point mutations without loss of cooperative function, have evidently evolved to permit conformational coupling in specified regions. The greater structural stability of the repeats in alphaII- and betaII-spectrin may account, at least in part, for the higher rigidity of brain compared to erythrocyte spectrin.

Animals↗
PubMed2006

Phosphorylation of a threonine unique to the short C-terminal isoform of betaII-spectrin links regulation of alpha-beta spectrin interaction to neuritogenesis.

Spectrin tetramers are cytoskeletal proteins required in the formation of complex animal tissues. Mammalian alphaII- and betaII-spectrin subunits form dimers that associate head to head with high affinity to form tetramers, but it is not known if this interaction is regulated. We show here that the short C-terminal splice variant of betaII-spectrin (betaIISigma2) is a substrate for phosphorylation. In vitro, protein kinase CK2 phosphorylates Ser-2110 and Thr-2159; protein kinase A phosphorylates Thr-2159. Antiphospho-Thr-2159 peptide antibody detected phosphorylated betaIISigma2 in Cos-1 cells. Immunoreactivity was increased in Cos-1 cells by treatment with forskolin, indicating that phosphorylation is promoted by elevated cAMP. The effect of forskolin was counteracted by the cAMP-dependent kinase inhibitor, H89. In vitro, protein kinase A phosphorylation of an active fragment of betaIISigma2 greatly reduced its interaction with alphaII-spectrin at the tetramerization site. Mutation of Thr-2159 to alanine eliminated inhibition by phosphorylation. Among the processes that require spectrin in mammals is the formation of neurites (incipient nerve axons). We tested the relationship of spectrin phosphorylation to neuritogenesis by transfecting the neuronal cell line, PC12, with enhanced green fluorescent protein-coupled fragments of betaIISigma2-spectrin predicted to act as inhibitors of spectrin tetramer formation. Both wild-type and T2159E mutant fragments allowed normal neuritogenesis in PC12 cells in response to nerve growth factor. The mutant T2159A inhibited neuritogenesis. Because the T2159A mutant represents a high affinity inhibitor of tetramer formation, we conclude that tetramers are requisite for neuritogenesis. Furthermore, because both the T2159E mutant and the wild-type allow neuritogenesis, we conclude that the short C-terminal betaII-spectrin is phosphorylated during this process.

Amino Acid Sequence↗
PubMed2006

Phosphatidylinositol-4,5-biphosphate (PIP2) differentially regulates the interaction of human erythrocyte protein 4.1 (4.1R) with membrane proteins.

Human erythrocyte protein 4.1 (4.1R) participates in organizing the plasma membrane by linking several surface-exposed transmembrane proteins to the internal cytoskeleton. In the present study, we characterized the interaction of 4.1R with phosphatidylinositol-4,5-bisphosphate (PIP2) and assessed the effect of PIP2 on the interaction of 4.1R with membrane proteins. We found that 4.1R bound to PIP2-containing liposomes through its N-terminal 30 kDa membrane-binding domain and PIP2 binding induced a conformational change in this domain. Phosphatidylinositol-4-phosphate (PIP) was a less effective inducer of this conformational change, and phosphatidylinositol (PI) and inositol-1,4,5-phosphate (IP3) induced no change. Replacement of amino acids K63,64 and K265,266 by alanine abolished the interaction of the membrane-binding domain with PIP2. Importantly, binding of PIP2 to 4.1R selectively modulated the ability of 4.1R to interact with its different binding partners. While PIP2 significantly enhanced the binding of 4.1R to glycophorin C (GPC), it inhibited the binding of 4.1R to band 3 in vitro. PIP2 had no effect on 4.1R binding to p55. Furthermore, GPC was more readily extracted by Triton X-100 from adenosine triphosphate (ATP)-depleted erythrocytes, implying that the GPC-4.1R interaction may be regulated by PIP2 in situ. These findings define an important role for PIP2 in regulating the function of 4.1R. Because 4.1R and its family members (4.1R, 4.1B, 4.1G, and 4.1N) are widely expressed and the PIP2-binding motifs are highly conserved, it is likely that the functions of other 4.1 proteins are similarly regulated by PIP2 in many different cell types.

Adenosine Triphosphate↗
PubMed2006

A FERM-adjacent (FA) region defines a subset of the 4.1 superfamily and is a potential regulator of FERM domain function.

BACKGROUND: Proteins containing FERM domains comprise a diverse group of eukaryotic proteins that bind membrane proteins and lipids. In doing so, they organise membrane microstructure, and coordinate the disposition of signalling and cell adhesion complexes. In protein 4.1R, phosphorylation adjacent to the FERM domain regulates its activity, and membrane mechanical properties. RESULTS: A novel sequence domain has been detected in a subset of proteins that contain FERM domains. This subset includes the true 4.1 proteins, some tyrosine phosphatases, rho-GEF proteins and type II transmembrane proteins, as well as some uncharacterised FERM proteins. This FERM-adjacent region is always closely proximate to the C-terminal of the FERM domain. This sequence is likely to be folded with elements of alpha and beta structure. The FERM-adjacent region of 4.1R contains serine residues phosphorylated by PKC and PKA; these appear conserved in about half of all other FERM-adjacent regions. Phylogenetic analyses indicate that all proteins containing a FERM-adjacent region arose from a single ancestor after FERM domains had started to proliferate in genomes of animals, plants and mycetozoa. CONCLUSION: The FERM-adjacent region defines a subset of the FERM proteins in animals. The conservation of motifs in this region that are potential substrates for kinases together with the known regulatory phosphorylation of 4.1R in this region raises the possibility that the FERM-adjacent region is a regulatory adaptation in this subset of the FERM proteins.

Amino Acid Motifs↗
PubMed2006

The transitional junction: a new functional subcellular domain at the intercalated disc.

We define here a previously unrecognized structural element close to the heart muscle plasma membrane at the intercalated disc where the myofibrils lead into the adherens junction. At this location, the plasma membrane is extensively folded. Immunofluorescence and immunogold electron microscopy reveal a spectrin-rich domain at the apex of the folds. These domains occur at the axial level of what would be the final Z-disc of the terminal sarcomere in the myofibril, although there is no Z-disc-like structure there. However, a sharp transitional boundary lies between the myofibrillar I-band and intercalated disc thin filaments, identifiable by the presence of Z-disc proteins, alpha-actinin, and N-terminal titin. This allows for the usual elastic positioning of the A-band in the final sarcomere, whereas the transduction of the contractile force normally associated with the Z-disc is transferred to the adherens junctions at the plasma membrane. The axial conjunction of the transitional junction with the spectrin-rich domains suggests a mechanism for direct communication between intercalated disc and contractile apparatus. In particular, it provides a means for sarcomeres to be added to the ends of the cells during growth. This is of particular relevance to understanding myocyte elongation in dilated cardiomyopathy.

Adherens Junctions↗
PubMed2006

Conformational stabilities of the structural repeats of erythroid spectrin and their functional implications.

The two polypeptide chains of the erythroid spectrin heterodimer contain between them 36 structural repeating modules, which can function as independently folding units. We have expressed all 36 and determined their thermal stabilities. These vary widely, with unfolding transition mid-points (T(m)) ranging from 21 to 72 degrees C. Eight of the isolated repeats are largely unfolded at physiological temperature. Constructs comprising two or more adjacent repeats show inter-repeat coupling with coupling free energies of several kcal mol(-1). Constructs comprising five successive repeats from the beta-chain displayed cooperativity and strong temperature dependence in forced unfolding by atomic force microscopy. Analysis of aligned sequences and molecular modeling suggests that high stability is conferred by large hydrophobic side chains at position e of the heptad hydrophobic repeats in the first helix of the three-helix bundle that makes up each repeat. This inference was borne out by the properties of mutants in which the critical residues have been replaced. The marginal stability of the tertiary structure at several points in the spectrin chains is moderated by energetic coupling with adjoining structural elements but may be expected to permit adaptation of the membrane to the large distortions that the red cell experiences in the circulation.

Cell Membrane↗
PubMed2006

Mammalian alpha I-spectrin is a neofunctionalized polypeptide adapted to small highly deformable erythrocytes.

Mammalian red blood cells, unlike those of other vertebrates, must withstand the rigors of circulation in the absence of new protein synthesis. Key to this is plasma membrane elasticity deriving from the protein spectrin, which forms a network on the cytoplasmic face. Spectrin is a tetramer (alphabeta)(2), made up of alphabeta dimers linked head to head. We show here that one component of erythrocyte spectrin, alphaI, is encoded by a gene unique to mammals. Phylogenetic analysis suggests that the other alpha-spectrin gene (alphaII) common to all vertebrates was duplicated after the emergence of amphibia, and that the resulting alphaI gene was preserved only in mammals. The activities of alphaI and alphaII spectrins differ in the context of the human red cell membrane. An alphaI-spectrin fragment containing the site of head-to-head interaction with the beta-chain binds more weakly than the corresponding alphaII fragment to this site. The latter competes so strongly with endogenous alphaI as to cause destabilization of membranes at 100-fold lower concentration than the alphaI fragment. The efficacies of alphaI/alphaII chimeras indicate that the partial structural repeat, which binds to the complementary beta-spectrin element, and the adjacent complete repeat together determine the strength of the dimer-dimer interaction on the membrane. Alignment of all available alpha-spectrin N-terminal sequences reveals three blocks of sequence unique to alphaI. Furthermore, human alphaII-spectrin is closer to fruitfly alpha-spectrin than to human alphaI-spectrin, consistent with adaptation of alphaI to new functions. We conclude that alphaI-spectrin represents a neofunctionalized spectrin adapted to the rapid make and break of tetramers.

Adaptation, Physiological↗
PubMed2005

Ankyrin-G in skeletal muscle: tissue-specific alternative splicing contributes to the complexity of the sarcolemmal cytoskeleton.

Ankyrins are versatile adaptor proteins that join the spectrin-based cytoskeleton to transmembrane proteins, and have roles in organizing the microstructure of cell membranes. Molecular diversity of ankyrins in mammals arises from extensive alternative splicing of the products of three genes. There has been no systematic analysis of the diversity of expression of ankyrins-G, the widely expressed Ank3 gene products, in a complex tissue. We previously described Ank(G107), the first muscle-specific ankyrin-G. Here, we combined cDNA and database analyses to gain novel insight into the ankyrins-G of skeletal muscle. We find: (i) that Ank3 is composed of at least 53 exons, many of which are subject to tissue-specific splicing; (ii) five novel full-length cDNAs encoding two canonical (Ank(G197), Ank(G217)) and three small isoforms (Ank(G109), Ank(G128), Ank(G130)) bring to six the number of ankyrins-G expressed in skeletal muscle; (iii) a 76-residue insert in the C-terminal domain is a 'signature' for muscle ankyrins; (iv) variably spliced sequences of 17/18 and 195 residues increase diversity in the C-terminal domains. Comparison of endogenous ankyrins-G with in vitro translated cDNAs revealed that small ankyrins account for the majority of the immunoreactivity for ankyrin-G in soleus muscle. The small ankyrins, when expressed in vivo in the rat muscle, are all targeted to sarcolemmal costameres. Our results demonstrate the tissue-dependent alternative splicing of Ank3 in skeletal muscle and point to novel functions of small ankyrins-G in organizing microdomains of the plasma membrane.

Alternative Splicing↗
PubMed2005

Predicting post-synaptic activity in proteins with data mining.

The bioinformatics problem being addressed in this paper is to predict whether or not a protein has post-synaptic activity. This problem is of great intrinsic interest because proteins with post-synaptic activities are connected with functioning of the nervous system. Indeed, many proteins having post-synaptic activity have been functionally characterized by biochemical, immunological and proteomic exercises. They represent a wide variety of proteins with functions in extracellular signal reception and propagation through intracellular apparatuses, cell adhesion molecules and scaffolding proteins that link them in a web. The challenge is to automatically discover features of the primary sequences of proteins that typically occur in proteins with post-synaptic activity but rarely (or never) occur in proteins without post-synaptic activity, and vice-versa. In this context, we used data mining to automatically discover classification rules that predict whether or not a protein has post-synaptic activity. The discovered rules were analysed with respect to their predictive accuracy (generalization ability) and with respect to their interestingness to biologists (in the sense of representing novel, unexpected knowledge).

Database Management Systems↗
PubMed2005

The spectrin-associated cytoskeleton in mammalian heart.

The membrane-associated cytoskeleton of the cardiac muscle cell is emerging as an important element in the maintenance of normal cell functioning. Recently it was shown that when proteins (betaII-spectrin, muscle Lim-only protein, ankyrin-B, ankyrin-G) of this system are defective or deficient, cardiac malfunction ensues. It is well-established that the spectrin cytoskeleton is associated with the plasma membrane, but it was only lately demonstrated that its components also lie on internal cell membranes. This is particularly apparent in muscle cells of the heart which contain specialised intracellular membrane compartments particular to this cell type such as the sarcoplasmic reticulum and T-tubules. Cardiomyocytes are subjected to constant mechanical stress. Since their mechanics are controlled through coordination of calcium fluxes mediated via cell membrane-based assemblies, it is imperative that these essential elements withstand the displacement forces of contraction. Cardiomyocyte spectrin locates the multifunctional spectrin/actin-binding and membrane-binding component, protein 4.1, and they act together on the plasma membrane as well as on internal membranes. We have found that cardiac protein 4.1 links to the calcium handling apparatus whilst spectrins connect with the sarcomeric contractile elements of the cell. Overall this assembly fulfils roles in stabilising cardiomyocyte cell membranes and in coordinating the macromolecular protein accumulations which regulate and accomplish cardiac molecular crosstalk, whilst at the same time enabling the muscle cells to resist extreme forces of contraction.

Animals↗
PubMed2005

Molecular evolution of ankyrin: gain of function in vertebrates by acquisition of an obscurin/titin-binding-related domain.

Ankyrins form a family of modular adaptor proteins that link between integral membrane proteins and the cytoskeleton. They evolved within the Metazoa as an adaptation for organizing membrane microstructure and directing membrane traffic. Molecular cloning has identified one Caenorhabditis elegans (unc-44), two Drosophila (Dank1, Dank2), and three mammalian (Ank1, Ank2, Ank3) genes. We have previously identified a 76-amino acid (aa) alternatively spliced sequence that is present in muscle polypeptides encoded by the rat Ank3 gene. A closely related sequence in a muscle Ank1 product binds the cytoskeletal muscle proteins obscurin and titin. This obscurin/titin-binding-related domain (OTBD) contains repeated modules of 18 aa: three are encoded by Ank1 and Ank2, two by Ank3; this pattern is conserved throughout vertebrate ankyrin genes. The C. elegans ankyrin, UNC-44, contains one 18-aa module as does the ankyrin gene in the urochordate Ciona intestinalis, but the insect ankyrins contain none. Our data indicate that an ancestral ankyrin acquired an 18-aa module which was preserved in the Ecdysozoa/deuterostome divide, but it was subsequently lost from arthropods. Successive duplications of the module led to a gain of function in vertebrates as it acquired obscurin/titin-binding activity. We suggest that the OTBD represents an adaptation of the cytoskeleton that confers muscle cells with resilience to the forces associated with vertebrate life.

Amino Acid Sequence↗
PubMed2005

Cardiac muscle cell cytoskeletal protein 4.1: analysis of transcripts and subcellular location--relevance to membrane integrity, microstructure, and possible role in heart failure.

The spectrin-based cytoskeleton assembly has emerged as a major player in heart functioning; however, cardiac protein 4.1, a key constituent, is uncharacterized. Protein 4.1 evolved to protect cell membranes against mechanical stresses and to organize membrane microstructure. 4.1 Proteins are multifunctional and, among other activities, link integral/signaling proteins on the plasma and internal membranes with the spectrin-based cytoskeleton. Four genes, EPB41, EPB41L1, EPB41L2, and EPB41L3 encode proteins 4.1R, 4.1N, 4.1G, and 4.1B, respectively. All are extensively spliced. Different isoforms are expressed according to tissue and developmental state, individual function being controlled through inclusion/exclusion of interactive domains. We have defined mouse and human cardiac 4.1 transcripts; other than 4. 1B in humans, all genes show activity. Cardiac transcripts constitutively include conserved FERM and C-terminal domains; both interact with membrane-bound signaling/transport/cell adhesion molecules. Variable splicing within and adjacent to the central spectrin/actin-binding domain enables regulation of cytoskeleton-binding activity. A novel heart-specific exon occurs in human 4.1G, but not in mouse. Immunofluorescence reveals 4.1 staining within mouse cardiomyocytes; thus, both at the plasma membrane and, interdigitated with sarcomeric myosin, across myofibrils in regions close to the sarcoplasmic reticulum. These are all regions to which spectrin locates. 4.1R in human heart shows similar distribution; however, there is limited plasma membrane staining. We conclude that cardiac 4.1s are highly regulated in their ability to crosslink plasma/integral cell membranes with the spectrin-actin cytoskeleton. We speculate that over the repetitive cycles of heart muscle contraction and relaxation, 4.1s are likely to locate, support, and coordinate functioning of key membrane-bound macromolecular assemblies.

Amino Acid Sequence↗
PubMed2005

Expression of human membrane skeleton protein genes for protein 4.1 and betaIISigma2-spectrin assayed by real-time RT-PCR.

The proteins, spectrin and 4.1 confer support and resilience to animal cell membranes, and promote assembly of multimeric, membrane-bound signalling complexes. Protein 4.1 also plays important roles in tumour suppression and the regulation of cell proliferation. To assess relative tissue expression of the four genes encoding human protein 4.1, we measured mRNA levels using quantitative real-time polymerase chain reaction. We compared 4.1 expression with that of a major splice variant of spectrin, betaIISigma2 that has a shortened C-terminus lacking a pleckstrin homology domain. mRNA for 4.1R is four-fold higher in bone marrow than in tissues with the next highest prevalence: cerebellum, lung, testis and thymus. 4.1G mRNA is highly expressed in brain, spinal cord and testis; 4.1N in brain, spinal cord and adrenal gland; 4.1B in testis, brain, spinal cord, and kidney. Thus, 4.1N, 4.1B and 4.1G all show high accumulation in nervous tissues. mRNA for betaIISigma2-spectrin is ubiquitous, but most abundant in cardiac and nervous tissues. Comparative transcript abundance was analysed in heart and brain. betaIISigma2-spectrin was the most abundant transcript in heart with levels 5 fold greater than 4.1G or 4.1N and at least 9 fold greater than 4.1B. In brain, 4.1N was the most abundant transcript, with levels 2.4 fold greater than 4.1B and at least 4 fold greater than 4.1G or betaIISigma2-spectrin. 4.1R abundance was very low in both tissues. Whilst we expected that 4.1 mRNAs would feature highly in muscle and nerve, we note their high abundance in testis, indicating previously unsuspected functions in reproduction.

Blood Proteins↗
PubMed2004

Not just a plasma membrane protein: in cardiac muscle cells alpha-II spectrin also shows a close association with myofibrils.

Spectrin and its associated proteins are essential for the integrity of muscle cells and there is increasing evidence for their involvement in signalling pathways as well as having a structural function in mediating stress. Spectrin is a multigene family and it is essential to determine which isoforms are present and their location in the cell. In heart muscle, we have found that one spectrin isoform, alphaII-spectrin, is strongly represented and, using immunofluorescence, we show that it lies within the contractile fibres near the Z-disc as well as on the cardiomyocyte plasma membrane. Electron microscopy of immunogold-labelled cryosections reveals statistically significant clustering of gold particles near the Z-disc, within and close to the edge of myofibrils. betaII-spectrin and ankyrin-R and G are both known to occupy this region. We suggest that alphaIIbetaII spectrin tetramers with ankyrin organise and/or stabilise cardiac muscle cell membrane components relative to the contractile apparatus.

Animals↗
PubMed2003

Spectrin alpha II and beta II isoforms interact with high affinity at the tetramerization site.

Spectrin tetramers form by the interaction of two alpha-beta dimers through two helices close to the C-terminus of a beta subunit and a single helix at the N-terminus of an alpha subunit. Early work on spectrin from solid tissues (typified by alphaII and betaII polypeptides) indicated that it forms a more stable tetramer than erythroid spectrin (alphaI-betaI). In the present study, we have probed the molecular basis of this phenomenon. We have quantified the interactions of N-terminal regions of two human alpha polypeptides (alphaI and alphaII) with the C-terminal regions of three beta isoforms (betaISigma1, betaIISigma1 and betaIISigma2). alphaII binds either betaII form with a much higher affinity than alphaI binds betaISigma1 ( K (d) values of 5-9 nM and 840 nM respectively at 25 degrees C). betaIISigma1 and betaIISigma2 are splice variants with different C-terminal extensions outside the tetramerization site: these extensions affect the rate rather than the affinity of alpha subunit interaction. alphaII spectrin interacts with each beta subunit with higher affinity than alphaI, and the betaII polypeptides have higher affinities for both alpha chains than betaISigma1. The first full repeat of the alpha subunit has a major role in determining affinity. Enthalpy changes in the alphaII-betaIISigma2 interaction are large, but the entropy change is comparatively small. The interaction is substantially reduced, but not eliminated, by concentrated salt solutions. The high affinity and slow overall kinetics of association and dissociation of alphaII-betaII spectrin may suit it well to a role in strengthening cell junctions and providing stable anchor points for transmembrane proteins at points specified by cell-adhesion molecules.

Binding Sites↗
PubMed2003

Distinct distribution of specific members of protein 4.1 gene family in the mouse nephron.

BACKGROUND: Protein 4.1 is an adapter protein that links the actin cytoskeleton to various transmembrane proteins. These 4.1 proteins are encoded by four homologous genes, 4.1R, 4.1G, 4.1N, and 4.1B, which undergo complex alternative splicing. Here we performed a detailed characterization of the expression of specific 4.1 proteins in the mouse nephron. METHODS: Distribution of renal 4.1 proteins was investigated by staining of paraformaldehyde-fixed mouse kidney sections with antibodies highly specific for each 4.1 protein. Major 4.1 splice forms, amplified from mouse kidney marathon cDNA, were expressed in transfected COS-7 cells in order to assign species of known exon composition to proteins detected in kidney. RESULTS: A 105 kD 4.1R splice form, initiating at ATG-2 translation initiation site and lacking exon 16, but including exon 17B, was restricted to thick ascending limb of Henle's loop. A 95 kD 4.1N splice form, lacking exons 15 and 17D, was expressed in either descending or ascending thin limb of Henle's loop, distal convoluted tubule, and all regions of the collecting duct system. A major 108 kD 4.1B splice form, initiating at a newly characterized ATG translation initiation site, and lacking exons 15, 17B, and 21, was present only in Bowman's capsule and proximal convoluted tubule (PCT). There was no expression of 4.1G in kidney. CONCLUSION: Distinct distribution of 4.1 proteins along the nephron suggests their involvement in targeting of selected transmembrane proteins in kidney epithelium and, therefore, in regulation of specific kidney functions.

Animals↗
PubMed2003

Comprehensive analysis of all triple helical repeats in beta-spectrins reveals patterns of selective evolutionary conservation.

The spectrin superfamily (spectrin, alpha-actinin, utrophin and dystrophin) has in common a triple helical repeating unit of ~106 amino acid residues. In spectrin, alpha and beta chains contain multiple copies of this repeat. beta-spectrin chains contain the majority of binding activities in spectrin and are essential for animal life. Canonical beta-spectrins have 17 repeats; beta-heavy spectrins have 30. Here, the repeats of five human beta-spectrins, plus beta-spectrins from several other vertebrates and invertebrates, have been analysed. Repeats 1, 2, 14 and 17 in canonical beta are highly conserved between invertebrates and vertebrates, and repeat 8 in some isoforms. This is consistent with conservation of critical functions, since repeats 1, 2 and 17 bind alpha-spectrin. Repeats 1 of beta-spectrins are not always detected by SMART or Pfam tools. A profile hidden Markov model of beta-spectrin repeat 1 detects alpha-actinins, but not utrophin or dystrophin. Novel examples of repeat 1 were detected in the spectraplakins MACF1, BPAG1 and plectin close to the actin-binding domain. Ankyrin binds to the C-terminal portion of repeat 14; the high conservation of this entire repeat may point to additional, undiscovered ligand-binding activities. This analysis indicates that the basic triple helical repeat pattern was adapted early in the evolution of the spectrin superfamily to encompass essential binding activities, which characterise individual repeats in proteins extant today.

Amino Acid Sequence↗