Effect of pH and salt bridges on structural assembly: Molecular structuresof the monomer and intertwined dimer of the Eps8 SH3 domain

Citation
Kvr. Kishan et al., Effect of pH and salt bridges on structural assembly: Molecular structuresof the monomer and intertwined dimer of the Eps8 SH3 domain, PROTEIN SCI, 10(5), 2001, pp. 1046-1055
Citations number
32
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Biochemistry & Biophysics
Journal title
PROTEIN SCIENCE
ISSN journal
0961-8368 → ACNP
Volume
10
Issue
5
Year of publication
2001
Pages
1046 - 1055
Database
ISI
SICI code
0961-8368(200105)10:5<1046:EOPASB>2.0.ZU;2-X
Abstract
The SH3 domain of Eps8 was previously found to form an intertwined, domain- swapped dimer. We report here a monomeric structure of the EPS8 SH3 domain obtained from crystals grown at low pH, as well as an improved domain-swapp ed dimer structure at 1.8 Angstrom resolution. In the domain-swapped dimer the asymmetric unit contains two "hybrid-monomers." In the low pH form ther e are two independently folded SH3 molecules per asymmetric unit. The forma tion of intermolecular salt bridges is thought to be the reason for the for mation of the dimer. On the basis of the monomer SH3 structure, it is argue d that Eps8 SH3 should, in principle, bind to peptides containing a PxxP mo tif. Recently it was reported that Eps8 SH3 binds to a peptide with a PxxDY motif. Because the "SH3 fold" is conserved, alternate binding sites may be possible for the PxxDY motif to bind. The strand exchange or domain swap o ccurs at the n-src loops because the n-src loops are flexible. The thermal b-factors also indicate the flexible nature of n-src loops and a possible h andle for domain swap initiation. Despite the loop swapping, the typical SH 3 fold in both forms is conserved structurally. The interface of the acidic form of SH3 is stabilized by a tetragonal network of water molecules above hydrophobic residues. The intertwined dimer interface is stabilized by hyd rophobic and aromatic stacking interactions in the core and by hydrophilic interactions on the surface.