title: The effect of cavity-filling mutations on the thermostability of Bacillus stearothermophilus neutral protease.
abstract: Cavities in the hydrophobic core of the neutral protease of Bacillus stearothermophilus were analyzed using a three-dimensional model that was inferred from the crystal structure of thermolysin, the highly homologous neutral protease of B. thermoproteolyticus (85% sequence identity). Site-directed mutagenesis was used to fill some of these cavities, thereby improving hydrophobic packing in the protein interior. The mutations had small effects on the thermostability, even after drastic changes, such as Leu284----Trp and Met168----Trp. The effects on T50, the temperature at which 50% of the enzyme is irreversibly inactivated in 30 min, ranged from 0.0 to +0.4 degrees C. These results can be explained by assuming that the mutations have positive and negative structural effects of approximately the same magnitude. Alternatively, it could be envisaged that the local unfolding steps, which render the enzyme susceptible towards autolysis and which are rate limiting in the process of thermal inactivation, are only slightly affected by alterations in the hydrophobic core.
authors.affiliation: Department of Genetics, University of Groningen, Haren, The Netherlands.
authors.forename: V G
authors.initials: VG
authors.lastname: Eijsink
authors.forename: B W
authors.initials: BW
authors.lastname: Dijkstra
authors.forename: G
authors.initials: G
authors.lastname: Vriend
authors.forename: J R
authors.initials: JR
authors.lastname: van der Zee
authors.forename: O R
authors.initials: OR
authors.lastname: Veltman
authors.forename: B
authors.initials: B
authors.lastname: van der Vinne
authors.forename: B
authors.initials: B
authors.lastname: van den Burg
authors.forename: S
authors.initials: S
authors.lastname: Kempe
authors.forename: G
authors.initials: G
authors.lastname: Venema
mesh_terms: D001483:Base Sequence; D004795:Enzyme Stability; D001411:Geobacillus stearothermophilus / Q000201:enzymology*; D008666:Metalloendopeptidases / Q000737:chemistry / Q000235:genetics*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D013696:Temperature
chemical_list: D008666:Metalloendopeptidases; C044194:microbial metalloproteinases