Thermodynamic properties of chitinase interaction with oligosaccharides

The intermolecular interactions involved in oligosaccharide-protein recognition, binding and cleavage are complex. Elucidation of these complex interactions is important in order to understand the biochemical role these proteins play. Fluorescence spectroscopy is a very good method to study the binding between a substrate and receptor. A non-native form (E315L) of the Family 18 Chitinase from the bacteria Serratia marcescens was produced and studied using fluorescence spectroscopy. Based upon the experimental data it is shown that the strength of binding ranges from –8.73 to – 12.19 kcal/mol with the trend in binding as GlcNAc3 < GlcNAc4 < GlcNAc5 = GlcNAc6. INTRODUCTION Chitin, a homopolysaccharide of β-(1 4)-linked N-acetylglucosamine (GlcNAc) is structurally the 2-amino sugar analogue of cellulose. Chitin acts as a major structural component in the exoskeleton of arthropods (Blackwell, 1969; Minke & Blackwell, 1978), and with the exception of cellulose, it is the second most prominent biopolymer found in nature. Biological degradation of chitin is difficult because its flat, board-like chains are densely packed through interchain hydrogen bonding into microcrystalline substrates. Adjacent chitin chains can run either parallel (β-chitin) (Blackwell, 1969) or, most commonly, anti-parallel (α-chitin) (Minke & Blackwell, 1978). In a chitin chain each GlcNAc is rotated 180° relative to its neighbor. Chitinases (EC 3.2.1.14) hydrolyze chitin β(1 4) linkages in order to make available the large quantities of carbon and nitrogen elements potentially trapped in the biosphere as insoluble GlcNAc (Keyhani & Roseman, 1999). Henrissat and Davies