Physicochemical characteristics of a thermostable gellan lyase from Geobacillus stearothermophilus 98

Abstract

A purifi ed thermostable gellan lyase, produced by a thermophilic bacterium, Geobacillus stearothermophilus 98, was characterized in relation to its physicochemical properties. The gellan lyase was established to have a molecular weight of 216 kDa, defi ned by capillary gel electrophoresis. Amino acid analysis revealed high quantities of Lys, His, Ala, Val, Ile, Glx, and Pro residues. The circular dichroism revealed 45% β-structure and practically lack of α-spiral domains. Kinetic studies showed high affi nity of the enzyme to gellan as a substrate (Km = 0.21 μM). The thermal denaturation investigated by cicular dichroism showed a highly cooperative transition with a midpoint (Tm) at about 75 °C. A single product was identify ed after enzyme action on gellan. Large exothermic aggregation near Tm was observed by differential scanning calorimetry. Two types of gellan lyase crystals were reproducibly isolated. © 2010 Verlag der Zeitschrift für Naturforschung, Tübingen.