Mass Spectrometric Sequence Studies of a Superoxide Dismutase from Bacillus stearothermophilus

Abstract

A partial sequence of the manganese-containing superoxide dismutase from Bacillus stearothermoplzilus has been determined by mass spectrometry. A new fragmentation reaction at N-terminal proline is described and an 'in-chain' fragmentation, also occurring at proline, has been observed. There is some evidence that the latter cleavage may also occur at other residues. Some differences from the classically determined sequence are reported, and the validity of these observations is discussed.Currently there are two strategies in use for the mass spectrometric determination of protein sequences. One requires the generation of small peptides (of two to five residues) and their derivatisation to 0-trimethylsilylated trifluoroacetyl-poly(amino alcohols). Separation and identification of these derivatives is accomplished by linked gas chromatography and mass spectrometry. This strategy has been successfully used in the sequencing of several proteins up to 250 amino acid residues [I -31.The other method involves the analysis of mixtures of acetyl, N-permethyl and 0-permethyl peptides, usually generated by the use of proteinases familar in conventional sequence work. This approach has also been applied to large proteins and is illustrated by the study of ribitol dehydrogenase [4].