Bacterial and archaeal endo-b-1,3-glucanases that belong to glycoside hydrolase family 16 share a b-jelly-roll fold, but differ significantly in sequence and in substrate specificity. The crystal structure of the laminarin-ase (EC ) from the hyperthermophilic archaeonPyrococcus furiosus (pfLamA) has been determined at A˚ resolution by molecular replace-ment. ThepfLamA structure reveals a kink of six residues (72–77) at the entrance of the catalytic cleft.