title: Non-zinc mediated inhibition of carbonic anhydrases: coumarins are a new class of suicide inhibitors.
abstract: The X-ray crystal structure of the adduct between the zinc metalloenzyme carbonic anhydrase II (CA, EC 4.2.1.1) with the recently discovered natural product coumarin derivative 6-(1S-hydroxy-3-methylbutyl)-7-methoxy-2H-chromen-2-one showed the coumarin hydrolysis product, a cis-2-hydroxy-cinnamic acid derivative, and not the parent coumarin, bound within the enzyme active site. The bound inhibitor exhibits an extended, two-arm conformation that effectively plugs the entrance to the enzyme active site with no interactions with the catalytically crucial zinc ion. The inhibitor is sandwiched between Phe131, with which it makes an edge-to-face stacking, and Asn67/Glu238sym, with which it makes several polar and hydrogen bonding interactions. This unusual binding mode, with no interactions between the inhibitor molecule and the active site metal ion is previously unobserved for this enzyme class and presents a new opportunity for future drug design campaigns to target a mode of inhibition that differs substantially from classical inhibitors such as the clinically used sulfonamides and sulfamates. Several structurally simple coumarin scaffolds were also shown to inhibit all 13 catalytically active mammalian CA isoforms, with inhibition constants ranging from nanomolar to millimolar. The inhibition is time dependent, with maximum inhibition being observed after 6 h.
authors.affiliation: Università degli Studi di Firenze, Laboratorio di Chimica Bioinorganica, Rm. 188, Via della Lastruccia 3, I-50019 Sesto Fiorentino, Florence, Italy.
authors.forename: Alfonso
authors.initials: A
authors.lastname: Maresca
authors.forename: Claudia
authors.initials: C
authors.lastname: Temperini
authors.forename: Hoan
authors.initials: H
authors.lastname: Vu
authors.forename: Ngoc B
authors.initials: NB
authors.lastname: Pham
authors.forename: Sally-Ann
authors.initials: SA
authors.lastname: Poulsen
authors.forename: Andrea
authors.initials: A
authors.lastname: Scozzafava
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Quinn
authors.forename: Claudiu T
authors.initials: CT
authors.lastname: Supuran
mesh_terms: D002257:Carbonic Anhydrase Inhibitors / Q000737:chemistry* / Q000494:pharmacology*; D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000378:metabolism; D003374:Coumarins / Q000737:chemistry* / Q000494:pharmacology*; D018360:Crystallography, X-Ray; D007527:Isoenzymes; D013058:Mass Spectrometry; D008958:Models, Molecular; D015032:Zinc / Q000737:chemistry
chemical_list: D002257:Carbonic Anhydrase Inhibitors; D003374:Coumarins; D007527:Isoenzymes; D002256:Carbonic Anhydrases; D015032:Zinc