XANES study of the carboxylate binding mode in two pterin hydroxylases.
The 2-His-1-carboxylate triad is an Fe(II)-binding motif common to several enzyme families. Within the catalytic cycle, the metal ion seems to alter between hexa- and pentacoordination, providing an open space in the Fe moiety for dioxygen binding. Anyhow, based on crystallographic studies, the picture is not fully consistent as different coordination numbers are reported for similar states. Moreover, the orientation of the metal-coordinating carboxylate varies in these studies. These differences are reflected in the XANES spectra analyzed in this paper. For isolated tyrosine and phenylalanine hydroxylase, the different active-site structures postulated by protein crystallography and further improved using spectroscopic data result in calculated XANES pattern that resemble very well the experiments. This work shows that structural differences in the non-coordinated oxygen of the carboxylate have no effect in the EXAFS but cause a change in the white-line intensity that can be successfully modeled within the muffin-tin approximation in small clusters. Thus, the study shows a way to analyze the 'carboxylate shift'. This highlights the potential of XANES analysis and clearly shows that the mentioned structural differences are present in solution as well, and does neither reflect the crystallization artifacts nor result from radiation damage or lacking resolution.
Mijovilovich
Ana
A
EMBL-Outstation Hamburg, Notkestrasse 85, Geb 25A, D-22603 Hamburg.|Present address: Department of Inorganic Chemistry and Catalysis, University of Utrecht, Sorbonnelaan 16, 3584CA, Utrecht, the Netherlands (phone: +31 30 253 4662; fax: +31 30 251 1027).
D015502:Absorptiometry, Photon; D002264:Carboxylic Acids; D018360:Crystallography, X-Ray; D006639:Histidine / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D006900:Hydroxylation; D019159:Nonheme Iron Proteins / Q000737:chemistry / Q000378:metabolism*; D010100:Oxygen / Q000378:metabolism; D010651:Phenylalanine Hydroxylase / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D011550:Pseudomonas aeruginosa / Q000201:enzymology; D011622:Pterins / Q000378:metabolism*; D014365:Tryptophan Hydroxylase / Q000378:metabolism; D014446:Tyrosine 3-Monooxygenase / Q000737:chemistry / Q000378:metabolism*
D002264:Carboxylic Acids; D019159:Nonheme Iron Proteins; D011622:Pterins; D006639:Histidine; D010651:Phenylalanine Hydroxylase; D014446:Tyrosine 3-Monooxygenase; D014365:Tryptophan Hydroxylase; D010100:Oxygen