Substrate recognition and selectivity of plant glycerol-3-phosphate acyltransferases (GPATs) from Cucurbita moscata and Spinacea oleracea

Stromal glycerol- 3- phosphate acyltransferases ( GPAT) are responsible for the selective incorporation of saturated and unsaturated fatty- acyl chains into chloroplast membranes, which is an important determinant of a plant's ability to tolerate chilling temperatures. The molecular mechanisms of plant chilling tolerance were elucidated by creating chimeric GPATs between squash ( Cucurbita moscata, chilling- sensitive) and spinach ( Spinacea oleracea, chilling- tolerant) and the results were interpreted using structural information on squash GPAT determined by X- ray crystallography at 1.55 Angstrom resolution. Enzymatic analysis of the chimeric GPATs showed that the chimeric GPATs containing the spinach region from residues 128 to 187 prefer the 18: 1 unsaturated fatty acid rather than 16: 0 saturated fatty acid. Structure analysis suggests that the size and character of the cavity that is formed from this region determines the specific recognition of acyl chains.