title: Carbonic anhydrase activators: kinetic and X-ray crystallographic study for the interaction of D- and L-tryptophan with the mammalian isoforms I-XIV.
abstract: An activation study of mammalian carbonic anhydrase (CA, EC 4.2.1.1) isoforms I-XIV with D- and L-tryptophan has been performed both by means of kinetic and X-ray crystallographic techniques. These compounds show a time dependent activity against isozyme CA II, with activation constants of 1.13 microM for L-Trp and 0.37 microM for D-Trp, respectively, after 24 h of incubation between enzyme and activator. The high resolution X-ray crystal structure of the hCA II-D-Trp adduct revealed the activator to bind in a totally unprecedented way to the enzyme active site as compared to histamine, L-/D-Phe, L-/D-His or L-adrenaline. D-Trp is anchored at the edge of the CA II active site entrance, strongly interacting with amino acid residues Asp130, Phe131 and Gly132 as well as with a loop of a second symmetry related protein molecule from the asymmetric unit, by means of hydrogen bonds and several weak van der Waals interactions involving Glu234, Gly235, Glu236 and Glu238. Thus, a second activator binding site (B) within the CA II cavity has been detected, where only D-Trp was shown so far to bind, in addition to the activator binding site A, in which histamine, L-/D-Phe, and L-/D-His are bound. These findings explain the strong affinity of D-Trp for CA II and may be useful for designing novel classes of CA activators by using this compound as lead molecule.
authors.affiliation: Università degli Studi di Firenze, Laboratorio di Chimica Bioinorganica, Room 188, Via della Lastruccia 3, I-50019 Sesto Fiorentino (Firenze), Italy.
authors.forename: Claudia
authors.initials: C
authors.lastname: Temperini
authors.forename: Alessio
authors.initials: A
authors.lastname: Innocenti
authors.forename: Andrea
authors.initials: A
authors.lastname: Scozzafava
authors.forename: Claudiu T
authors.initials: CT
authors.lastname: Supuran
mesh_terms: D002256:Carbonic Anhydrases / Q000737:chemistry* / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray / Q000379:methods*; D020536:Enzyme Activators / Q000737:chemistry* / Q000378:metabolism; D004837:Epinephrine / Q000737:chemistry / Q000378:metabolism; D006632:Histamine / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D010649:Phenylalanine / Q000737:chemistry / Q000378:metabolism; D011487:Protein Conformation; D020033:Protein Isoforms / Q000737:chemistry* / Q000378:metabolism; D013237:Stereoisomerism; D014364:Tryptophan / Q000737:chemistry / Q000378:metabolism
chemical_list: D020536:Enzyme Activators; D020033:Protein Isoforms; D010649:Phenylalanine; D006632:Histamine; D014364:Tryptophan; D002256:Carbonic Anhydrases; D004837:Epinephrine