The gene encoding a type I pullulanase was identified from the genome sequence of the anaerobic thermoalkaliphilic bacterium Anaerobranca gottschalkii. In addition, the homologous gene was isolated from a gene library of Anaerobranca horikoshii and sequenced. The proteins encoded by these two genes showed 39% amino acid sequence identity to the pullulanases from the thermophilic anaerobic bacteria Fervidobacterium pennivorans and Thermotoga maritima. The pullulanase gene from A. gottschalkii (encoding 865 amino acids with a predicted molecular mass of 98 kDa) was cloned and expressed in Escherichia coli strain BL21(DE3) so that the protein did not have the signal peptide. Accordingly, the molecular mass of the purified recombinant pullulanase (rPulAg) was 96 kDa. Pullulan hydrolysis activity was optimal at pH 8.0 and 70°C, and under these physicochemical conditions the half-life of rPulAg was 22 h. By using an alternative expression strategy in E. coli Tuner(DE3)(pLysS), the pullulanase gene from A. gottschalkii, including its signal peptide-encoding sequence, was cloned. In this case, the purified recombinant enzyme was a truncated 70-kDa form (rPulAg). The N-terminal sequence of purified rPulAg was found 252 amino acids downstream from the start site, presumably indicating that there was alternative translation initiation or N-terminal protease cleavage by E. coli. Interestingly, most of the physicochemical properties of rPulAg were identical to those of rPulAg. Both enzymes degraded pullulan via an endo-type mechanism, yielding maltotriose as the final product, and hydrolytic activity was also detected with amylopectin, starch, -limited dextrins, and glycogen but not with amylose. This substrate specificity is typical of type I pullulanases. rPulAg was inhibited by cyclodextrins, whereas addition of mono-or bivalent cations did not have a stimulating effect. In addition, rPulAg was stable in the presence of 0.5% sodium dodecyl sulfate, 20% Tween, and 50% Triton X-100. The pullulanase from A. gottschalkii is the first thermoalkalistable type I pullulanase that has been described.Pullulanases (pullulan 6-glucanohydrolase; EC 3.2.1.41) are debranching enzymes that are able to hydrolyze the ␣-1,6 bonds of the linear ␣-glucan pullulan, producing maltotriose as the final product. Pullulanases are divided into two classes based on substrate specificity: (i) type I pullulanases or debranching enzymes, which specifically hydrolyze the ␣-1,6 linkages in branched oligosaccharides, such as starch, amylopectin, and glycogen, forming linear ␣-1,4-linked oligomers; and (ii) type II pullulanases or amylopullulanases, which cleave ␣-1,6 glycosidic linkages in pullulan and branched substrates in addition to the ␣-1,4 glycosidic linkages in polysaccharides other than pullulan (7).A number of pullulanases have been purified from different bacterial and archaeal sources and characterized. Most enzymes from thermophilic and hyperthermophilic microorganisms are type II pullulanases (35,42,50,52) and have been isolated mainly from ...
