Attachment of Metal-chelating Functional Groups to Hen Egg White Lysozyme

A possible approach to the preparation of heavy atom-containing protein crystals through covalent attachment of a metal-chelating group to the protein is described. The reactions of lysozyme and guanidinated lysozyme with methyl picolinimidate are shown to introduce 6.6 to 7 and 1.1 to 1.3 picolinimidinyl groups, respectively, into the protein molecule by reaction of the reagent with the amino groups converting them to picolinamidine functions. Studies with model picolinamidines reported here and by others show that the picolinamidine group strongly chelates d orbital transition metal ions. Both of the derivatives of lysozyme can be induced to form large crystals under suitable conditions, and both possess considerable lytic activity.