Structural basis of substrate and inhibitory activity of bovine plasma amine oxidase.

摘要

The copper-containing amine oxidases, like bovine plasma amine oxidase (BPAO), carry out a transaminative oxidation of primary amines to aldehydes via use of an active site Tyr-derived 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor. Propargylamine is a potent inactivator of BPAO (IC50 = 3 muM), possibly through active-site modification by the alpha,beta-unsaturated aldehyde turnover product, but the simple structure is expected to confer low selectivity. On the basis of the finding by previous students that certain extended conjugation analogs such as 1,6-diamino-2,4-hexadiyne and 3-cyanopropargylamine preserve strong inactivation potency, other extended conjugation analogs of propargylamine were evaluated. In particular, 1-amino-2,4-hexadiynes with a 6-OH rather than 6-NH2 group were found to be potent inhibitors.; Structure-substrate relationships for a broad family of monoamines, diamines, and polyamines were investigated to reveal information on the binding modes to BPAO. The results indicated that (i) monoamines only bind to the hydrophobic wall at the entrance to the active site, (ii) the alkyl chain of long-chain diamines (≥8 carbons) would also bind to the hydrophobic region near the active site, while their terminal amino groups can interact electrostatically with D445', (iii) the medium-chain diamines (6-7 carbons) were moderate substrates because their alkyl tether can barely extend beyond the hydrophobic region and can only interact weakly with D445', (iv) short chain diamines (≤5 carbons) are weak substrates because the terminal amino groups in these cases would reside in a hydrophobic region that prefers neutral groups, (v) triamines like spermidine will bind to the enzyme with the middle amino group being neutral, and where the terminal amino groups should have favorable electrostatic interactions with the D445' if the total chain length is sufficiently long, and (vi) one of the internal amino groups (AM2) of spermine should be neutral for optimal binding to the enzyme, where the AM3 and AM4 should have interaction with D445' and D179, respectively, in their protonated form.; The bis-quaternary diamines are found to be a new class of potent competitive inhibitors of BPAO. The bis-quaternary diamines are proposed to bind to two ancillary cation binding sites: D445' and D179, in contrast to only one binding site for monoquaternary amines. The longer chain bis-quaternary diamines have higher inhibitory potency, suggesting that their alkyl tethers can have some hydrophobic interactions with the hydrophobic region between D445' and D179, and this region is different from the hydrophobic "wall" to which monoamines bind.; The C3-alkyl-extended analogs of propargylamine were evaluated and their inhibitory potencies were found to be much lower than propargylamine itself, though the methyl- and ethyl-extended analogs exhibited higher substrate activity than propargylamine. This result prompted an evaluation of possible high substrate activity for other analogs of potent mechanism-based inhibitors that displayed anomalously low inhibitory potency. The results showed that there is no obviously predictable correlation between substrate activity and inhibitory potency.; A series of 3-(trialkylsilyl)propargylamines were investigated as possible pro-drugs for delivery of propargylamine as an inhibitor of copper amine oxidases. The mechanism involves hydrolysis of the acetylenic C-Si bond. The hydrolysis speed and the aqueous/lipid distribution can be adjusted by variation of the alkyl substituents on silicon.