The glucokinase regulatory protein (GCKR) []is a vertebrate protein thatinhibits glucokinase by forming a complex with the enzyme, which plays a rolein the control of blood glucose homeostasis. GCKR is a protein of about 70 Kdwhich is evolutionary related to bacterial N-acetylmuramic acid 6-phosphateetherases (MurNAc-6-P etherase, murQ), which are about half the size of GCKRand form active homodimers. MurNAc-6-P etherases catalyse the cleavage of theD-lactyl ether substituent of the bacterial cell wall sugar MurNAc and play arole in recycling of the cell wall []. The 3D structure of the Haemophilusinfluenzae HI0754/murQ protein shows structural relationshipswith other sugar isomerase (SIS) domain proteins. Incontrast to mono-SIS bacterial MurNAc-6-P etherase, mammalian GCKR is composedof two SIS domains.
