INHIBITION OF THERMOLYSIN AND NEUTRAL ENDOPEPTIDASE-24.11 BY A NOVEL GLUTARAMIDE DERIVATIVE - X-RAY STRUCTURE DETERMINATION OF THE THERMOLYSIN INHIBITOR COMPLEX

Determination of the X-ray structure of thermolysin-inhibitor complexe s has proven useful in aiding our understanding of the mode of binding of inhibitors of related, physiologically important, mammalian zinc p eptidases including neutral endopeptidase EC 3.4.24.11 and angiotensin -converting enzyme. Here we describe the mode of binding to crystallin e thermolysin of 4-phenylbutyl)-cyclopentylcarbonyl}-(S)-tryptophan (C CT). CCT is an analogue of both candoxatrilat, a potent inhibitor of n eutral endopeptidase 24.11, and of the 5-indanyl ester prodrug candoxa tril, which is under clinical evaluation as a potential therapy for co ngestive heart failure. CCT differs from the previously studied N-carb oxyalkyl dipeptide CLT carboxy-3-phenylpropyl)-(S)-leucyl-(S)-tryptoph an] in several important respects. It has a highly constrained gem-cyc lopentyl P1' substituent and lacks the characteristic imino nitrogen s ubstituent of CLT. The structure determination shows that, notwithstan ding the conformational influence of the gem-cyclopentyl substituent, CCT binds within the active site of thermolysin in a similar manner to CLT. Although the characteristic hydrogen bond between the imino nitr ogen of CLT and thermolysin is absent in CCT, the affinities of the tw o inhibitors for the enzyme are virtually identical. These results ill ustrate the importance of considering not only those hydrogen bonds th at are formed in an enzyme-ligand complex but also the other hydrogen bonds that may be lost due to desolvation of the enzyme and ligand on formation of the complex. In addition, the overall conformational dema nds placed upon a ligand in order to achieve receptor interaction may be critically important.