title: Nickel(II)-substituted azurin I from Alcaligenes xylosoxidans as characterized by resonance Raman spectroscopy at cryogenic temperature.
abstract: Metal-substituted blue copper proteins (cupredoxins) have been successfully used to study the effect of metal-ion identity on their active-site properties, specifically the coordination geometry and metal-ligand bond strengths. In this work, low-temperature (77 K) resonance Raman (RR) spectra of the blue copper protein Alcaligenes xylosoxidans azurin I and its Ni(II) derivative are reported. A detailed analysis of all observed bands is presented and responsiveness to metal substitution is discussed in terms of structural and bonding changes. The native cupric site exhibits a RR spectrum characteristic of a primarily trigonal planar (type 1) coordination geometry, identified by the nu(Cu-S)(Cys) markers at 373, 399, 409, and 430 cm(-1). Replacement of Cu(II) with Ni(II) results in optical and RR spectra that reveal (1) a large hypsochromic shift in the main (Cys)S --> M(II) charge-transfer absorption from 622 to 440 nm, (2) greatly reduced metal-thiolate bonding interaction, indicated by substantially lower nu(Ni-S)(Cys) stretching frequencies, (3) elevation of the cysteine nu(C( beta )-S) stretching, amide III, and rho (s)(C( beta )H(2)) scissors vibrational modes, and (4) primarily four-coordinated, trigonally distorted tetrahedral geometry of the Ni(II) site that is marked by characteristic nu(Ni-S)(Cys) stretching RR bands at 347, 364, and 391 cm(-1). Comparisons of the electronic and vibrational properties between A. xylosoxidans azurin I and its closely structurally related azurin from Pseudomonas aeruginosa are made and discussed. For cupric azurins, the intensity-weighted average M(II)-S(Cys) stretching frequencies are calculated to be nu(Cu-S)(iwa) = 406.3 and 407.6 cm(-1), respectively. These values decreased to nu(Ni-S)(iwa) = 359.3 and 365.5 cm(-1), respectively, after Ni(II) --> Cu(II) exchange, suggesting that the metal-thiolate interactions are similar in the two native proteins but are much less alike in their Ni(II)-substituted forms.
authors.affiliation: Department of Chemistry, University of Houston, Houston, TX 77204-5003, USA.
authors.forename: Marzena B
authors.initials: MB
authors.lastname: Fitzpatrick
authors.forename: Roman S
authors.initials: RS
authors.lastname: Czernuszewicz
mesh_terms: D000421:Alcaligenes / Q000737:chemistry*; D001400:Azurin / Q000737:chemistry*; D001426:Bacterial Proteins / Q000737:chemistry; D003080:Cold Temperature; D009532:Nickel / Q000737:chemistry*; D013059:Spectrum Analysis, Raman / Q000379:methods*
chemical_list: D001426:Bacterial Proteins; D001400:Azurin; D009532:Nickel