Tyrosine Raman signatures of the filamentous virus Ff are diagnostic of non-hydrogen-bonded phenoxyls: demonstration by Raman and infrared spectroscopy of p-cresol vapor.
p-Cresol is a simple molecular model for the para phenolic side chain of tyrosine. Previously, Siamwiza and co-workers [(1975) Biochemistry 14, 4870-4876] investigated p-cresol solutions to identify Raman spectroscopic signatures for different hydrogen-bonding states of the tyrosine phenoxyl group in proteins. They found that the phenolic moiety exhibits an intense Raman doublet in the spectral interval 820-860 cm(-1) and that the doublet intensity ratio (I2/I1, where I2 and I1 are Raman peak intensities of the higher- and lower-wavenumber members of the doublet) is diagnostic of specific donor and acceptor roles of the phenoxyl OH group. The range of the doublet intensity ratio in proteins (0.30 < I2/I1 < 2.5) was shown to be governed by Fermi coupling between the phenolic ring-stretching fundamental nu1 and the first overtone of the phenolic ring-deformation mode nu(16a), such that when the tyrosine phenoxyl proton is a strong hydrogen-bond donor, I2/I1 = 0.30, and when the tyrosine phenoxyl oxygen is a strong hydrogen-bond acceptor, I2/I1 = 2.5. Here, we interpret the Raman and infrared spectra of p-cresol vapor and extend the previous correlation to the non-hydrogen-bonded state of the tyrosine phenoxyl group. In the absence of hydrogen bonding, the Raman intensity of the higher-wavenumber component of the canonical Fermi doublet is greatly enhanced such that I2/I1 = 6.7. Thus, for the non-hydrogen-bonded phenoxyl, the lower-wavenumber member of the Fermi doublet loses most of its Raman intensity. This finding provides a basis for understanding the anomalous Raman singlet signature (approximately 854 cm(-1)) observed for tyrosine in coat protein subunits of filamentous viruses Ff and Pf1 [Overman, S. A., et al. (1994) Biochemistry 33, 1037-1042; Wen, Z. Q., et al. (1999) Biochemistry 38, 3148-3156]. The implications of the present results for Raman analysis of tyrosine hydrogen-bonding states in other proteins are considered.
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Department of Chemistry, Texas A&M University, College Station, Texas 77843-3255, USA.
Autrey
D
D
Laane
J
J
Overman
S A
SA
Thomas
G J
GJ
D002213:Capsid / Q000737:chemistry; D003408:Cresols / Q000737:chemistry*; D005609:Free Radicals / Q000737:chemistry; D006358:Hot Temperature; D006860:Hydrogen Bonding; D017912:Inovirus / Q000737:chemistry*; D010636:Phenols / Q000737:chemistry*; D013055:Spectrophotometry, Infrared / Q000379:methods; D013059:Spectrum Analysis, Raman / Q000379:methods; D013696:Temperature; D014443:Tyrosine / Q000737:chemistry*; D014835:Volatilization
D003408:Cresols; D005609:Free Radicals; D010636:Phenols; C032538:4-cresol; C042329:phenoxy radical; D014443:Tyrosine