Mechanism of the Very Efficient Quenching of Tryptophan Fluorescence in Human γD- and γS-Crystallins: The γ-Crystallin Fold May Have Evolved To Protect Tryptophan Residues from Ultraviolet Photodamage†

Proteins exposed to UV radiation are subject to irreversible photodamage through covalent modification of tryptophans (Trps) and other UV-absorbing amino acids. Crystallins, the major protein components of the vertebrate eye lens that maintain lens transparency, are exposed to ambient UV radiation throughout life. The duplicated β-sheet Greek key domains of β- and γ-crystallins in humans and all other vertebrates each have two conserved buried Trps. Experiments and computation showed that the fluorescence of these Trps in human γD-crystallin is very efficiently quenched in the native state by electrostatically enabled electron transfer to a backbone amide [Chen et al. (2006) Biochemistry 45, 11552−11563]. This dispersal of the excited state energy would be expected to minimize protein damage from covalent scission of the excited Trp ring. We report here both experiments and computation showing that the same fast electron transfer mechanism is operating in a different crystallin, human γS-crystallin. Examination of solved structures of other crystallins reveals that the Trp conformation, as well as favorably oriented bound waters, and the proximity of the backbone carbonyl oxygen of the n − 3 residues before the quenched Trps (residue n), are conserved in most crystallins. These results indicate that fast charge transfer quenching is an evolved property of this protein fold, probably protecting it from UV-induced photodamage. This UV resistance may have contributed to the selection of the Greek key fold as the major lens protein in all vertebrates.National Eye Institute (Grant EY 015834

Pregnancy-related pelvic girdle pain: an update

A large number of scientists from a wide range of medical and surgical disciplines have reported on the existence and characteristics of the clinical syndrome of pelvic girdle pain during or after pregnancy. This syndrome refers to a musculoskeletal type of persistent pain localised at the anterior and/or posterior aspect of the pelvic ring. The pain may radiate across the hip joint and the thigh bones. The symptoms may begin either during the first trimester of pregnancy, at labour or even during the postpartum period. The physiological processes characterising this clinical entity remain obscure. In this review, the definition and epidemiology, as well as a proposed diagnostic algorithm and treatment options, are presented. Ongoing research is desirable to establish clear management strategies that are based on the pathophysiologic mechanisms responsible for the escalation of the syndrome's symptoms to a fraction of the population of pregnant women

QUENCHING STUDIES ON LASER EXCITED IODINE VAPOR

This research was supported by the Petroleum Research Fund. $^{1}$ S. Ezckiel and R. Weiss, Phys. Rev. Letters 20 (3), 91 (1968). $^{2}$ R. Gordon, J. Chem. Phys. 45, 1643-1648 (1966).Author Institution: Department of Chemistry, Massachusetts Institute of TechnologyThe fluorescence of iodine vapor corresponding to the transition $B^{3}\Pi_{o_{u}+}- X^{1}\Sigma_{o_{u}+}$ was studied at room temperature $(20^{\circ}C)$ using a pulsed argon ion laser as the excitation source. An assignment was made for the levels reached by the argon excitation. It was found that the following lines in the iodine absorption spectrum overlapped with the $5145.36 {\AA}$ argon line: $(51-1), P(53); (50-1), P(39); (49-1), P(18): (43-0), P(12), R(14); (45-0), P(64)$. The occurrence of the $v^{\prime} = 43$ and $v^{\prime} = 49$ band series in the fluorescence agrees with the assignment of Ezekiel and $Weiss^1$ in their work on laser induced fluorescence in an iodine molecular beam. Quenching cross sections were measured for a variety of inert gases, including He, Ne, Ar, Xe, and Kr; and from the study of the fluorescence side bands, vibrational-rotational energy transfer cross sections were determined. Self quenching cross sections for iodine vapor were also measured, taking into account the self-absorption of radiation. The depolarization of individual rotational lines in the resolved spectrum at low pressure in the presence of foreign gases will be discussed with reference to the molecular reorientation on collision, along the lines formulated by $Gordon.^{2}