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Role of the IXI/V motif in oligomer assembly and function of StHsp14.0, a small heat shock protein from the acidothermophilic archaeon, Sulfolobus tokodaii strain 7
Author(s) -
Saji Hitoshi,
Iizuka Ryo,
Yoshida Takao,
Abe Tetsuya,
Kidokoro Shunichi,
Ishii Noriyuki,
Yohda Masafumi
Publication year - 2007
Publication title -
proteins: structure, function, and bioinformatics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.699
H-Index - 191
eISSN - 1097-0134
pISSN - 0887-3585
DOI - 10.1002/prot.21762
Subject(s) - oligomer , chaperone (clinical) , biochemistry , peptide sequence , biology , heat shock protein , amino acid , mutant , chemistry , gene , polymer chemistry , medicine , pathology
Abstract Small heat shock proteins (sHsps) are one of the most ubiquitous molecular chaperones. They are grouped together based on a conserved domain, the α‐crystallin domain. Generally, sHsps exist as oligomers of 9–40 subunits, and the oligomers undergo reversible temperature‐dependent dissociation into smaller species as dimers, which interact with denaturing substrate proteins. Previous studies have shown that the C‐terminal region, especially the consensus IXI/V motif, is responsible for oligomer assembly. In this study, we examined deletions or mutations in the C‐terminal region on the oligomer assembly and function of StHsp14.0, an sHsp from an acidothermophilic archaeon, Sulfolobus tokodaii strain 7. Mutated StHsp14.0 with C‐terminal deletion or replacement of IIe residues in the IXI/V motif to Ala, Ser, or Phe residues could not form large oligomers and lost chaperone activity. StHsp14.0WKW, whose Ile residues in the IXI/V motif are changed to Trp, existed as an oligomer like that of the wild type. However, it dissociates to small oligomers and exhibits chaperone activity at relatively lowered temperature. Replacement of two Ile residues in the motif to relatively small residues, Ala or Ser, also resulted in the change of β‐sheet rich secondary structure and decrease of hydrophobicity. Interestingly, StHsp14.0 mutant with amino acid replacements to Phe kept almost the same secondary structure and relatively high hydrophobicity despite that it could not form an oligomeric structure. The results show that hydrophobicity and size of the amino acids in the IXI/V motif in the C‐terminal region are responsible not only for assembly of the oligomer but also for the maintenance of β‐sheet rich secondary structure and hydrophobicity, which are important for the function of sHsp. Proteins 2008. © 2007 Wiley‐Liss, Inc.