Functional analysis of a gene encoding homoserine kinase from rice

Abstract

Homoserine kinase (HSK) is an enzyme that catalyzes the common pathway in threonine and methionine biosynthesis in plants. The genes encoding HSK have been reported in many bacteria and some plants including Arabidopsis. Our group recently reported a gene for threonine synthase (TS) from rice. In this study, we functionally characterized a gene encoding HSK from rice (OsHSK). Analysis of a cDNA sequence and genome of rice revealed that a full-length open leading frame of OsHSK consisted of 378 amino acids, which corresponded to a protein with the molecular weight of approximately 37.8 kDa and with the predicted isoelectric point of 6.86. The predicted amino acid sequence of OsHSK harbored a distinct signature motif for ATP binding and was highly homologous to that of enzymes of plant and bacterial HSKs. Expression of OsHSK in the thrB mutant of Escherichia coli showed that the gene was able to functionally complement the mutant. These results suggest that OsHSK encodes a protein for HSK in rice.

Keywords: Homoserine, homoserine kinase, rice (Oryza sativa), thrB