N1,N1-Diethyl-N 2-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)acetamidine

Abstract

The PII proteins from the cyanobacteria Synechococcus sp. PCC 7942 and Synechocystis sp. PCC 6803 have been crystallized and high-resolution structures have been obtained using X-ray crystallography. The core of these new structures is similar to that of the PII proteins from Escherichia coli, although the structures of the T- and C-loops differ. The T-loop of the Synechococcus protein is ordered, but appears to be stabilized by crystal contacts. The same loop in the Synechocystis protein is disordered. The C-terminus of the Synechocystis protein is stabilized by hydrogen bonding to the same region of a crystallographically related molecule. The same terminus in the Synechococcus protein is stabilized by coordination with a metal ion. These observations are consistent with the idea that both the T-loop and the C-terminus of PII proteins are ¯exible in solution and that this ¯exibility may be important for receptor recognition. Sequence comparisons are used to identify regions of the sequence unique to the cyanobacteria