Structural and functional studies of Ectoine Synthase from Chromohalobacter salexigens DSM 3043 and Marinobacter sp. CK1

Abstract

Ectoine is a compatible solute found in many microorganisms adapted to survive in saline and other extreme environments. Here, it aids microorganisms to counter osmotic stress and protect their enzymes. Ectoine exhibit many interesting properties that is potentially commercially exploitable, and it is currently produced and found in several products on the market. While ectoine is produced by whole cell synthesis, the EctABC enzymes in the biosynthesis pathway of ectoine was currently not well described structurally or functionally. Here, we present structural and biochemical characterizations of ectoine synthase from two organisms, Chromohalobacter salexigens DSM3043 and Marinobacter sp. CK1. We cloned, expressed and expression optimized both candidates, and purified them by immobilized metal affinity chromatography and gel filtration. C. salexigens EctC (CSEctC) yielded 14-18 mg/L cell culture while Marinobacter sp. CK1 (MarEctC) yielded 0.75-1.5 mg/L culture. We then produced diffracting crystals of CSEctC and obtained a data set from which the structure of CSEctC was determined. We further obtained preliminary biochemical data relating to thermostability and activity from both candidates. The crystal structure from CSEctC shows that it is adapts a typical β-sandwich fold, consistent with earlier structural investigations of other EctC type proteins. This study provides a solid foundation for further research on EctC from our model organisms, and protocols and techniques developed herein can be further optimized to obtain more biochemical data about this interesting enzyme.