Characterization of different crystal forms of the α-­glucosidase MalA from Sulfolobus solfataricus

MalA is an α-glucosidase from the hyperthermophilic archaeon Sulfolobus solfataricus. It belongs to glycoside hydrolase family 31, which includes several medically interesting α-glucosidases. MalA and its selenomethionine derivative have been overproduced in Escherichia coli and crystallized in four different crystal forms. Microseeding was essential for the formation of good-quality crystals of forms 2 and 4. For three of the crystal forms (2, 3 and 4) full data sets could be collected. The most suitable crystals for structure determination are the monoclinic form 4 crystals, belonging to space group P2₁, from which data sets extending to 2.5 Å resolution have been collected. Self-rotation functions calculated for this form and for the orthorhombic (P2₁2₁2₁) form 2 indicate the presence of six molecules in the asymmetric unit related by 32 symmetry.