Glutamine synthetase regulation, adenylylation state, and strain specificity analyzed by polyacrylamide gel electrophoresis

Abstract

We used polyacrylamide gel electrophoresis to examine the regulation and adenylylation states of glutamine synthetases (GSs) from Escherichia coli (GS(E)) and Klebsiella aerogenes (GS(K)). In gels containing sodium dodecyl sulfate (SDS), we found that GS(K) had a mobility which differed significantly from that of GS(E). In addition, for both GS(K) and GS(E), adenylylated subunits (GS(K)-adenosine 5'-monophosphate [AMP] and GS(E)-AMP) had lesser mobilities in SDS gels than did the corresponding non-adenylylated subunits. The order of mobilities was GS(K)-AMP < GS(K) < GS(E)-AMP < GS(E). We were able to detect these mobility differences with purified and partially purified preparations of GS, crude cell extracts, and whole cell lysates. SDS gel electrophoresis thus provided a means of estimating the adenylylation state and the quantity of GS present independent of enzymatic activity measurements and of determining the strain origin. Using SDS gels, we showed that: (i) the constitutively produced GS in strains carrying the glnA4 allele was mostly adenylylated, (ii) the GS-like polypeptide produced by strains carrying the glnA51 allele was indistinguishable from wild-type GS(K), and (iii) strains carrying the glnA10 allele contained no polypeptide having the mobility of GS(K) or GS(K)-AMP. Using native polyacrylamide gels, we detected the increased amount of dodecameric GS present in cells grown under nitrogen limitation compared with cells grown under conditions of nitrogen excess. In native gels there was neither a significant difference in the mobilities of adenylylated and non-adenylylated GSs nor a GS-like protein in cells carrying the glnA10 allele.