PDBsum entry 1dav

Hydrolase

PDB id

1dav

Contents

			Protein chain

					71 a.a. *

			Metals

					_CA ×2

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Solution structure of a type i dockerin domain, A novel prokaryotic, Extracellular calcium-Binding domain.

Authors

B.L.Lytle, B.F.Volkman, W.M.Westler, M.P.Heckman, J.H.Wu.

Ref.

J Mol Biol, 2001, 307, 745-753. [DOI no: 10.1006/jmbi.2001.4522]

PubMed id

11273698

Abstract

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.



	Figure 2. Figure 2. (a) Superposition of the backbone atoms (N, C^a and C') of the selected 20 Ct-Doc structures. The structures are superimposed against the mean structure using residues 5 to 29 and 32 to 66. The a-helices are shown in cyan and the turn of 3[10] helix is highlighted green. Calcium ions are shown as yellow spheres. (b) Ribbon diagram of the energy-minimized averaged structure. (c) Side-view of Ct-Doc (ribbon representation), with the interacting hydrophobic side-chains comprising the two clusters shown in red and green, and the conserved Val15 and Val47 (loop position 8) shown in yellow. All structural representations were generated with the program MOLMOL. [43]		Figure 3. Figure 3. Comparison of the topology of (a) Ct-Doc and (b) C-terminal domain of cardiac muscle troponin C (PDB code 3CTN).