PubMed · 4471121
The source did not provide an abstract. Follow the original record for more information.
Explore connections, maps & timelines
J Kumate. 1974. [Immunoglobulins: structure and functions].. https://pubmed.ncbi.nlm.nih.gov/4471121/
Cite the original work for its findings. Save a collection to share your selection of sources.
KEEP EXPLORING
The goal of this work is to define the structural and sequence features common to sandwich-like proteins (SPs), a group of very different proteins now comprising 69 superfamilies in 38 protein folds. Analysis of the arrangements of strands within main sandwich sheets revealed a rigorously defined constraint on the supersecondary substructure that holds true for 94% of known SP structures. The invariant substructure consists of two interlocked pairs of neighboring beta-strands. It is even more typical for centers of SP than the well-known "Greek key" strands arrangement for their edges. As homology among these proteins is not usually detectable even with the most powerful sequence-comparing algorithms, we employed a structure-based approach to sequence alignment. Within the interlocked strands we found 12 positions with fixed structural roles in SP. A residue at any of these positions possesses similar structural properties with residues in the same position of other SPs. The 12 positions lie at the center of the interface between the beta-sheets and form the common geometrical core of SPs. Of the 12 positions, 8 are occupied by only four hydrophobic residues in 80% of all SPs.
The structural and dynamic properties of an immunoglobulin superfamily domain (IgSF), Ig 18', have been characterised by NMR at 285 K, in the presence of 4.2 M and 6.0 M urea, respectively. Analysis of chemical shift deviations, 3JHNHalpha coupling constants, sequential NOE pattern, and 15N relaxation data reveals that although the two urea-denatured states are highly disordered, some local turn-like residual structures do exist. Moreover, some distinct differences between the properties of the two denatured states are observed. In 4.2 M urea-denatured Ig 18', regions 80-83 and 86-92 adopt turn-like conformations, furthermore, region 84-93 is involved in slow exchange processes that occur on a micro- to millisecond time-scale. In the 6.0 M urea-denatured state, these turn-like conformations are less occupied, and chemical exchange processes in region 84-93 are largely reduced. In contrast, region 32-36 has persistent turn-like structures in both urea-denatured states. Some correlation between the spectral density function at 0 frequency, Jeff(0), for the urea-denatured states and the secondary structure elements of the folded state have been observed. Except for the terminal regions, residues corresponding to beta-strands have higher Jeff(0) values compared to residues corresponding to loops. The characterisation and comparison of the two urea-denatured states highlight residues that possess properties that may be crucial for the initiation of folding of this domain.
Expression and purification of the extracellular portion of granulocyte colony-stimulating factor (G-CSF) receptor, which contains an immunoglobulin-like (Ig) domain and the cytokine receptor homologous (CRH) region, using a baculovirus secretion system have shown that a tetrameric Ig-CRH protein (about 200 kDa) existed in addition to the dimer (85 kDa) [7]. Scatchard analysis revealed that the tetramer had ligand binding affinity, with a dissociation constant of about 2.5 nM. The tetramer dissociated into monomers at pH 2 and was re-formed at pH7, in contrast, the dimer was re-dimerized with the same treatment. These observations led us to hypothesize the existence of conformational heterogeneity, which leads to tetramer as well as dimer formation, in the soluble state of the Ig-CRH protein.