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Oligomerization into multimeric complexes is a prerequisite for the chaperone function of almost all a-crystallin type heat shock proteins (a-Hsp), but the molecular details of complex assembly are poorly understood. The a-Hsp proteins from Bradyrhizobium japonicum are suitable bacterial models for structure-function studies of these ubiquitous stress proteins. They fall into two distinct classes, A and B, display chaperone activity in vitro and form oligomers of 24 subunits. | Eur. J. Biochem. 269 3578-3586 2002 FEBS 2002 doi 10.1046 j.1432-1033.2002.03049.x A critical motif for oligomerization and chaperone activity of bacterial a-heat shock proteins Sonja Studer Markus Obrist Nicolas Lentze and Franz Narberhaus Institute of Microbiology Eidgenossische Technische Hochschule Zurich Switzerland Oligomerization into multimeric complexes is a prerequisite for the chaperone function of almost all a-crystallin type heat shock proteins a-Hsp but the molecular details of complex assembly are poorly understood. The a-Hsp proteins from Bradyrhizobium japonicum are suitable bacterial models for structure-function studies of these ubiquitous stress proteins. They fall into two distinct classes A and B display chaperone activity in vitro and form oligomers of w 24 subunits. We constructed 19 derivatives containing truncations or point mutations within the N- and C-terminal regions and analyzed them by gel filtration citrate synthase assay and coaffinity purification. Truncation of more than the initial few ami no acids ol Ihe N-temiinal region e d to the formation of distinct dimeric to octameric structures devoid of chaperone activity. In the C-terminal extension integrity of an isoleucine-X-isoleucine I-X-I motif was imperative for a-Hsp functionality. This I-X-I motif is one of the characteristic consensus motifs of the a-Hsp family and here we provide experimental evidence of its structural and functional importance. a-Hsp proteins lacking the C-termi-nal extension were inactive but still able to form dimers. Here we demonstrate that the central a-crystallin domain alone is not sufficient for dimerization. Additional residues at the end of the N-terminal region were required for the assembly of two subunits. Keywords a-crystallin a-heat shock protein small heat shock protein chaperone oligomerization. Heat shock or other forms of stress induce the expression of a-heat shock proteins a-Hsp proteins in a broad range of prokaryotic and eukaryotic .
