PACKING SELECTION OF BACILLUS-LENTUS SUBTILISIN AND A SITE-SPECIFIC VARIANT

The crystallization of a variant of Bacillus lentus subtilisin and the native enzyme was achieved using identical conditions. The variant B. lentus was found to grow in two crystal forms, form 1 and form 2, whe reas the native B. lentus subtilisin enzyme crystallized in only one, form 1. Form 2 crystals, once obtained, were found to grow much more r apidly than form 1 crystals. The lattice contacts and structural chang es giving both crystal forms have been examined. The results show that crystal form 2 has a more complex network of interactions. There is a lso a small surface conformational change in the form 2 structure rela tive to the native and variant form 1 crystals and at least two solven t molecules bound to the enzyme in crystal form 1 are displaced in cry stal form 2. In addition, a site specific substitution in the variant at position 27 induces a 'short' lattice contact which does not exist in the native B. lentus or the form 2 variant B. lentus. These results suggest that in some circumstances engineered variants could be desig ned to crystallize more rapidly than the native enzyme.