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Metal–ligand interactions in azido, cyano and thiocyanato adducts of Pseudomonas aeruginosa Met121X (X=Gly, Ala, Val or Leu) azurins monitored by resonance Raman spectroscopy
Author(s) -
Fraczkiewicz Grazyna,
Bonander Nicklas,
Czernuszewicz Roman S.
Publication year - 1998
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/(sici)1097-4555(199810/11)29:10/11<983::aid-jrs335>3.0.co;2-u
Subject(s) - chemistry , adduct , crystallography , raman spectroscopy , resonance raman spectroscopy , resonance (particle physics) , azide , stereochemistry , physics , organic chemistry , particle physics , optics
Cryogenic‐temperature (77 K) resonance Raman (RR) spectroscopy and 15 N and 13 C isotope substitutions were used todetermine vibrational mode wavenumbers associated withCu II —N 3 ‐ ,Cu II —CN ‐ andCu II —SCN ‐ units for azido, cyano andthiocyanato adducts of Pseudomonas aeruginosa Met121X (whereX=Gly, Ala, Val or Leu) azurins, and to evaluate the structuralinfluences of Met121 mutation and binding of exogenous ligands on thetype 1 Cu site. The spectra of Met121X azurins indicate that the Cusite retains its planar trigonal geometry upon Met121 mutations toLeu, Val and Ala, but undergoes a tetrahedral distortion with aslightly extended Cu—S(Cys) bond upon mutation to Gly. Theprotein–anion adducts displayed RR spectra characteristic of thestrongly tetrahedrally distorted Cu centers with dramatically reduced(by 50–70 cm ‐1 ) ν(Cu–S Cys )stretching wavenumbers and, consequently, greatly diminishedCu–S(Cys) interactions when compared with the uncomplexedproteins. Two azide‐related modes in theM121A–N 3 ‐ adduct are observed at 375 and2024 cm ‐1 and assigned as the ν(Cu–N 3 )and ν as (N 3 ) stretching modes based upon 15/14 N 3 isotopic shifts (‐8 and ‐67cm ‐1 , respectively). Their counterparts in the Gly, Val andLeu variants occur near 371 and 2045 cm ‐1 , suggesting aweaker azide interaction with the Cu site than in the Ala variant. Anearly complete set of the thiocyanato‐bound vibrational wavenumbersafforded by RR spectra of M121V–SCN ‐ permittedaccurate band assignments based on the observedS 13 CN ‐ and SC 15 N ‐ isotopeshifts and the results of normal coordinate analysis. In particular,the characteristic ν(S–C) ( ca . 720 cm ‐1 )and ν(C≡N) ( ca . 2100 cm ‐1 ) stretchingwavenumbers establish that SCN ‐ binds to the metal via theS atom to give a planar Cu—S—C≡N moiety. We alsofind that CN ‐ coordinates to the copper via its carbon atomgiving rise to two 13 CN‐sensitive weak bands atapproximately 277 and 398 cm ‐1 , assigned as theν(Cu–C) stretch and the δ(Cu–C≡N) bend,respectively. © 1998 John Wiley & Sons, Ltd.