Crystal structures of human glutaminyl cyclase, an enzyme responsible for protein N-terminal pyroglutamate formation.

N-terminal pyroglutamate (pGlu) formation from its glutaminyl (or glutamyl) precursor is required in the maturation of numerous bioactive peptides. The aberrant formation of pGlu may be related to several pathological processes, such as osteoporosis and amyloidotic diseases. This N-terminal cyclization reaction, once thought to proceed spontaneously, is greatly facilitated by the enzyme glutaminyl cyclase (QC). To probe this important but poorly understood modification, we present here the structure of human QC in free form and bound to a substrate and three imidazole-derived inhibitors. The structure reveals an alpha/beta scaffold akin to that of two-zinc exopeptidases but with several insertions and deletions, particularly in the active-site region. The relatively closed active site displays alternate conformations due to the different indole orientations of Trp-207, resulting in two substrate (glutamine t-butyl ester)-binding modes. The single zinc ion in the active site is coordinated to three conserved residues and one water molecule, which is replaced by an imidazole nitrogen upon binding of the inhibitors. Together with structural and kinetic analyses of several active-site-mutant enzymes, a catalysis mechanism of the formation of protein N-terminal pGlu is proposed. Our results provide a structural basis for the rational design of inhibitors against QC-associated disorders.

A study of human annexin V derivative: its effects of anticoagulation and antithrombosis / 中华血液学杂志

<p><b>OBJECTIVE</b>To investigate the effects of a new anticoagulant, annexin V derivative (AND) on anticoagulation and antithrombosis.</p><p><b>METHODS</b>High and low doses of AND were given to rabbits (groups 1 and 2 respectively) by intravenous (iv) bolus injections followed by half the respective AND doses by iv infusion over 2 hours. Control groups were iv given heparin (group 3) and saline (group 4) of the same volume and procedure as that in group 1 and 2. Blood cell count, activated partial thromboplastin time (APTT), prothrombin time (PT), thrombin time (TT) and fibrinogen level were examined before and 15, 30 and 60 min after iv bolus and 2 hours after the end of iv infusion. A 3.0 mm x 15 mm balloon was put into femoral artery to induce endothelial denudation 15 min after IV bolus and the blood pressure of femoral artery was monitored until the pulse pressure recorded 0 mm Hg when the vessel was occluded completely by a thrombus. The femoral arteries were collected and the thrombi were stripped off for measuring their lengths, wet and dry weights.</p><p><b>RESULTS</b>Anticoagulation parameters: APTT at 15 min after iv bolus in AND group was significantly longer than that in group 4 (P < 0.05) but shorter than that in group 3 (P < 0.05); APTT and TT in group 3 were significantly longer than those in groups 1, 2 and 4. Fibrinogen: 0.70 mg/kg AND may decrease fibrinogen. Antithrombosis values: the wet and dry weights in AND groups were significantly lighter than those in group 3 and 4 (P < 0.05). The dry weight in high-dose AND group was remarkably lighter than that in low-dose group (P = 0.029). The length of thrombus in low-dose AND group was remarkably shorter than that in group 4 (P = 0.013), but not for group 3 (P > 0.05). It was remarkably shorter in high-dose AND group than in both group 3 (P < 0.001) and 4 (P = 0.015). The time when pulse pressure equaled to 0 was longer in AND group than in group 4 (P < 0.05), but not in 3.</p><p><b>CONCLUSION</b>AND is an effective anticoagulant and antithrombosis agent, the highest anticoagulation effect occurs at 15 min after IV bolus. Its anticoagulation effect is not more potent than that of standard heparin, while antithrombosis capacity is more effective. AND in treating thrombosis clinically might be promising.</p>