A critical motif for oligomerization and chaperone activity of bacterial alpha-heat shock proteins.
Oligomerization into multimeric complexes is a prerequisite for the chaperone function of almost all alpha-crystallin type heat shock proteins (alpha-Hsp), but the molecular details of complex assembly are poorly understood. The alpha-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 approximately 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 amino acids of the N-terminal region led 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 alpha-Hsp functionality. This I-X-I motif is one of the characteristic consensus motifs of the alpha-Hsp family, and here we provide experimental evidence of its structural and functional importance. alpha-Hsp proteins lacking the C-terminal extension were inactive, but still able to form dimers. Here, we demonstrate that the central alpha-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.
Studer
Sonja
S
Institute of Microbiology, Eidgenössische Technische Hochschule, Zürich, Switzerland.
Obrist
Markus
M
Lentze
Nicolas
N
Narberhaus
Franz
F
D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D020369:Bradyrhizobium / Q000378:metabolism*; D002950:Citrate (si)-Synthase / Q000737:chemistry; D003459:Crystallins / Q000737:chemistry; D019281:Dimerization; D006360:Heat-Shock Proteins / Q000737:chemistry* / Q000502:physiology; D007532:Isoleucine / Q000737:chemistry; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017510:Protein Folding; D025941:Protein Interaction Mapping; D011993:Recombinant Fusion Proteins / Q000502:physiology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship
D003459:Crystallins; D006360:Heat-Shock Proteins; D046911:Macromolecular Substances; D011993:Recombinant Fusion Proteins; D007532:Isoleucine; D002950:Citrate (si)-Synthase