Lytle B L, Volkman B F, Westler W M, Heckman M P, Wu J H
Department of Chemical Engineering, University of Rochester, NY 14627-0166, USA.
J Mol Biol. 2001 Mar 30;307(3):745-53. doi: 10.1006/jmbi.2001.4522.
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.
I型dockerin结构域负责通过与纤维素体支架亚基的受体结构域（粘着蛋白结构域）相互作用，将其相关的糖基水解酶整合到细菌纤维素体（一种多酶纤维素分解复合物）中。高度保守的dockerin结构域的特征是有两个与EF-手基序序列相似的Ca(2+)结合位点。在此，我们展示了嗜热栖热菌纤维二糖水解酶CelS的69个残基的dockerin结构域的三维溶液结构。利用总共728个源自NOE的距离约束和79个扭转角约束进行的扭转角动力学计算，得到了20个结构的集合，5至29位和32至66位残基的平均主链均方根偏差与平均结构相差0.54 Å。该结构由通过一个连接子连接的两个Ca(2+)结合环-螺旋基序组成；dockerin结构域中不存在进入经典EF-手基序每个环的E螺旋。每个dockerin Ca(2+)结合亚结构域由一簇埋藏的疏水侧链稳定。结构比较表明，在其非复合状态下，dockerin折叠与Ca(2+)结合的EF-手结构域有显著差异。提出了一个由保守的疏水和碱性残基组成的假定粘着蛋白结合表面，为纤维素体组装提供了新的见解。
