title: Modelling the site of bromide binding in vanadate-dependent bromoperoxidases.
abstract: Treatment of Boc-protected (S)-serine (Ser) methyl ester with triphenylphosphine bromide Ph(3)PBr (intermittently generated from PPh(3) and N-bromosuccinimide) yields Boc-3-bromoalanine (R)-Boc-BrAlaMe and, after deprotection, bromoalanine methyl ester (R)-BrAlaMe in the form of its hydrobromide. Boc-BrAlaMe and BrAlaMe have been structurally characterised. The reaction between BrAlaMe, salicylaldehyde (sal) and VO(2+) results in the formation of Schiff base complexes of composition [VO(sal-BrAlaMe)solv](+) (solv = CH(3)OH: 3, THF: 5) and [VO(sal-BrAla)THF] 4. DFT calculations of the structures of 3, 4 and 5, based on the B3LYP functional and employing the triple zeta basis set 6-311++g(d,p), provide distances Br···V = 4.0 ± 0.1 Å, if some distortion of the dihedral angle ∠N-C-C-Br is allowed (affording a maximum energy of ca. 45 kJ mol(-1)), and thus model Br···V distances detected by X-ray methods in bromoperoxidases from the marine algae Ascophyllum nodosum and Corallina pilulifera. The DFT calculations have been validated by comparing calculated and found structures, including the new complex [V(V)O(Amp-sal)OMe(MeOH)] (1, Amp is the aminophenol moiety) and the known complex [VO(L-Ser-van)H(2)O] (van = vanillin). Additional validation has been undertaken by checking experimental against calculated (BHandHLYP) EPR spectroscopic hyperfine coupling constants. Complexes containing bromine as a substituent at the phenyl moiety of a Schiff base ligand do not allow for an appropriate simulation of the Br···V distance in peroxidases. The closest agreement, d(Br···V) = 4.87 Å, is achieved with [VO(3Br-salSer)THF] (6), where 3Brsal-Ser is the dianionic Schiff base formed between 3-Br-5-NO(2)-salicylaldehyde and serine.
authors.affiliation: Chemistry Department, University of Hamburg, D-20147 Hamburg, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Kraehmer
authors.forename: Dieter
authors.initials: D
authors.lastname: Rehder
mesh_terms: D000409:Alanine / Q000737:chemistry / Q000378:metabolism; D044646:Ascophyllum / Q000201:enzymology; D001665:Binding Sites; D001965:Bromides / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D008968:Molecular Conformation; D010544:Peroxidases / Q000737:chemistry* / Q000378:metabolism; D015203:Reproducibility of Results; D012545:Schiff Bases / Q000737:chemistry; D013237:Stereoisomerism; D014638:Vanadates / Q000378:metabolism*
chemical_list: D001965:Bromides; D012545:Schiff Bases; D014638:Vanadates; D010544:Peroxidases; C026195:bromide peroxidase; D000409:Alanine