Solution structure of a type I dockerin domain, a novel prokaryotic, extracellular calcium-binding domain.
The type I dockerin domain is responsible for incorporating its associated glycosyl hydrolase into the bacterial cellulosome, a multienzyme cellulolytic complex, via its interaction with a receptor domain (cohesin domain) of the cellulosomal scaffolding subunit. The highly conserved dockerin domain is characterized by two Ca(2+)-binding sites with sequence similarity to the EF-hand motif. Here, we present the three-dimensional solution structure of the 69 residue dockerin domain of Clostridium thermocellum cellobiohydrolase CelS. Torsion angle dynamics calculations utilizing a total of 728 NOE-derived distance constraints and 79 torsion angle restraints yielded an ensemble of 20 structures with an average backbone r.m.s.d. for residues 5 to 29 and 32 to 66 of 0.54 A from the mean structure. The structure consists of two Ca(2+)-binding loop-helix motifs connected by a linker; the E helices entering each loop of the classical EF-hand motif are absent from the dockerin domain. Each dockerin Ca(2+)-binding subdomain is stabilized by a cluster of buried hydrophobic side-chains. Structural comparisons reveal that, in its non-complexed state, the dockerin fold displays a dramatic departure from that of Ca(2+)-bound EF-hand domains. A putative cohesin-binding surface, comprised of conserved hydrophobic and basic residues, is proposed, providing new insight into cellulosome assembly.
Department of Chemical Engineering, University of Rochester, NY 14627-0166, USA.
B L
BL
Lytle
B F
BF
Volkman
W M
WM
Westler
M P
MP
Heckman
J H
JH
Wu
D000595:Amino Acid Sequence; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002480:Cellulase / Q000737:chemistry* / Q000378:metabolism*; D043366:Cellulose 1,4-beta-Cellobiosidase; D002868:Chromosomal Proteins, Non-Histone; D003013:Clostridium / Q000201:enzymology*; D020832:EF Hand Motifs; D005656:Fungal Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D009687:Nuclear Proteins / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D000097722:Cohesins
D002118:Calcium; D018797:Cell Cycle Proteins; D002480:Cellulase; D043366:Cellulose 1,4-beta-Cellobiosidase; D002868:Chromosomal Proteins, Non-Histone; D005656:Fungal Proteins; D009687:Nuclear Proteins; D000097722:Cohesins; C071223:endoglucanase Ss