Biomedical subjects

Susanne Gräslund

Publications and source records attributed to Susanne Gräslund.

4 recordsLinked to original sources

PubMed2006

Crystal structure of human inosine triphosphatase. Substrate binding and implication of the inosine triphosphatase deficiency mutation P32T.

Inosine triphosphatase (ITPA) is a ubiquitous key regulator of cellular non-canonical nucleotide levels. It breaks down inosine and xanthine nucleotides generated by deamination of purine bases. Its enzymatic action prevents accumulation of ITP and reduces the risk of incorporation of potentially mutagenic inosine nucleotides into nucleic acids. Here we describe the crystal structure of human ITPA in complex with its prime substrate ITP, as well as the apoenzyme at 2.8 and 1.1A, respectively. These structures show for the first time the site of substrate and Mg2+ coordination as well as the conformational changes accompanying substrate binding in this class of enzymes. Enzyme substrate interactions induce an extensive closure of the nucleotide binding grove, resulting in tight interactions with the base that explain the high substrate specificity of ITPA for inosine and xanthine over the canonical nucleotides. One of the dimer contact sites is made up by a loop that is involved in coordinating the metal ion in the active site. We predict that the ITPA deficiency mutation P32T leads to a shift of this loop that results in a disturbed affinity for nucleotides and/or a reduced catalytic activity in both monomers of the physiological dimer.

Amino Acid Substitution↗

PubMed2002

A novel affinity gene fusion system allowing protein A-based recovery of non-immunoglobulin gene products.

An expression vector system has been developed, taking advantage of a novel, Staphylococcus aureus protein A (SPA)-binding affinity tag Z(SPA-1), enabling straightforward affinity blotting procedures and efficient recovery by affinity purification of expressed gene products on readily available reagents and chromatography media. The 58 amino acid SPA-binding affinity tag Z(SPA-1), was previously selected from a library constructed by combinatorial mutagenesis of a protein domain from SPA. An Escherichia coli expression vector for intracellular T7 promoter (P(T7)) driven production was constructed with an N-terminal dual affinity tag, consisting of a hexahistidyl (His(6)) tag in frame with the Z(SPA-1) tag, thus allowing alternative affinity recovery methods. To evaluate the system, five cDNA clones from a mouse testis cDNA library were expressed, and two alternative blotting procedures were developed for convenient screening of expression efficiencies. The five produced fusion proteins were recovered on both immobilized metal-ion affinity chromatography (IMAC) columns and on Protein A-based chromatography media, to allow comparative studies. It was found that the Protein A-based recovery resulted in the highest degree of purity, and furthermore, gene products that were produced as inclusion bodies could after denaturation be efficiently affinity purified on Protein A-Sepharose in the presence of 0.5 M guanidine hydrochloride. The convenience and robustness of the presented expression system should make it highly suitable for various high-throughput protein expression efforts.

Amino Acid Sequence↗

PubMed2002

Single-vector three-frame expression systems for affinity-tagged proteins.

An effort is presented to create expression vectors which would allow expression of an inserted gene fragment in three reading frames in a single vector from a single promoter but with three separate ribosome binding sites (RBS). Each expression frame would generate an in-frame fusion with an affinity tag to allow efficient recovery of the produced fusion proteins. In the first generation vector, three identical polyhistidyl tags (His(6)) were used as affinity tags for the three expression frames. In the second generation vector, three different tags, an albumin binding domain derived from streptococcal protein G, an IgG binding Staphylococcus aureus protein A-derived domain (Z) and a His(6) tag, were employed to allow frame-specific affinity recovery. To evaluate the systems, model genes have been inserted in three different frames in both vectors. The first vector was demonstrated to produce fusion proteins in all three frames, whereas for the second, with a much wider spacing between the RBSs and affinity tags, expression could only be demonstrated from the first two translational start sites. For both systems, the first translation start was found to be significantly favored over the others. Nevertheless, we believe that the presented results represent the first successful attempt to create single-vector three-frame expression systems, a concept that could become valuable in future combined cloning-expression vectors.

Bacterial Proteins↗

PubMed2002

A high-stringency proteomics concept aimed for generation of antibodies specific for cDNA-encoded proteins.

A novel dual bacterial expression system, designed for high-throughput generation of antibodies specific for cDNA-encoded proteins, is presented. The concept involves parallel expression of cDNA-encoded proteins, in two vector systems, as fusions with two different tags, both enabling single-step affinity purification under denaturing conditions. One of the fusion tags includes a portion with documented immunopotentiating effect to stimulate antibody production, and the generated fusion proteins are used to elicit antibodies. The second fusion protein is used in an immobilized form as an affinity ligand to enrich, from the generated antisera, antibodies with selective reactivity to the cDNA-encoded part. To evaluate the system, five cDNA clones from a mouse testis cDNA library were expressed, and antibodies to these cDNA-encoded proteins were generated, enriched and used in blotting procedures to determine expression patterns for the native proteins corresponding to the cDNAs. The five antibody preparations showed specific reactivity to the corresponding recombinant cDNA-encoded proteins, and three of the five antibodies gave specific staining in Western-blot screening of various cell types and tissue homogenates. When the same five cDNAs were processed and analysed using a single-vector method, antibodies with a more non-specific staining were generated. We thus conclude that the presented dual-vector method offers a highly stringent strategy for generation of monospecific polyclonal antibodies.

Animals↗