Modeling Studies of an Exotype Alginate Lyase Atu3025 from Agrobacterium Tumefaciens Strain C58, a Member of Polysaccharide Lyase Family 15

Abstract

Alginate lyases, also known as alginases or alginate depolymerases, catalyze the degradation of alginate by a -elimination mechanism that has yet to be fully elucidated. Alginate is a copolymer of -L-guluronate (G) and its C5 epimer -D-mannuronate (M), arranged as homopolymeric G blocks, M blocks, alternating GM or random heteropolymeric G/M stretches. Almost all alginate lyases depolymerize alginate in an endolytical fashion via a -elimination reaction. The alginate lyase Atu3025 from Agrobacterium tumefaciens strain C58, consisting of 776 amino-acid residues, is a novel exotype alginate lyase classified into polysaccharide lyase family 15. Till now there is no crystal structure available for this class of proteins. Since there is no template with high sequence identity, three-dimensional coordinates for exotype alginate lyase (PL 15 family) were determined using modeling methods (Comparitive modeling and Fold recognition). The structures were modeled using the X-ray coordinates from Heparinase protein family (PDB code: 3E7J). This enzyme (Atu3025) displays enzymatic activity for both poly-M and poly-G alginate. Since poly-M is widespread; docking of a tri-mannuronate against the modeled structure was performed. We identified some of those residues which are crucial for lyase activity. The results from this study should guide future mutagenesis studies and also provides a starting point for further proceedings.