Crystal structures of two cyanobacterial response regulators in apo- and phosphorylated form reveal a novel dimerization motif of phytochrome-associated response regulators.

The structures of two response regulators (RRs) from the cyanobacterium Calothrix PCC7601, RcpA and RcpB, were solved to 1.9- and 1.75-A resolution, respectively. RcpA was found in phosphorylated and RcpB in nonphosphorylated form. Both RRs are members of phytochrome-associated, light-sensing two-component signal transduction pathways, based on histidine kinase-mediated receptor autophosphorylation and phosphorelay to a RR. Despite the overall folding similarity to CheY-type RRs ((beta/alpha)(5)-motif), RcpA and RcpB form homodimers, irrespective of their phosphorylation state, giving insight into a signal transduction putatively different from that of other known RRs. Dimerization is accomplished by a C-terminal extension of the RR polypeptide chain, and the surface formed by H4, beta 5, and H5, which constitute a hydrophobic contact area with distinct interactions between residues of either subunit. Sequence alignments reveal that the identified dimerization motif is archetypal for phytochrome-associated RRs, making them a novel subgroup of CheY-type RRs. The protein structures of RcpA and RcpB are compared to the recently presented protein structure of Rcp1 from Synechocystis.

FTIR studies of phytochrome photoreactions reveal the C=O bands of the chromophore: consequences for its protonation states, conformation, and protein interaction.

The molecular changes of phytochrome during red --> far-red and reverse photoreactions have been monitored by static infrared difference spectroscopy using the recombinant 65 kDa N-terminal fragment assembled with a chromophore chemically modified at ring D or with a chromophore isotopically labeled with (18)O at the carbonyl group of ring A. This allows the identification of the C=O stretching vibrations of rings D and A. We exclude the formation of an iminoether in Pfr. The positions of both these modes show that the chromophore always remains protonated. The upshift of the C=O stretch of ring D in the first photoproducts is explained by a twisted methine bridge connecting rings C and D. The changes in the vibrational pattern during the red --> far-red conversion show that the backreaction is not just the reversal of the forward reaction. The infrared difference spectra of the fragment deviate very little from those of the full-length protein. The differences which are related to the lack of the C-terminal half of the protein constituting the signaling domain are possibly important for the understanding of the signaling mechanism.

Emergency medicine. The rural challenge.

Overcrowding, stress-related job burnout for emergency room physicians and other personnel, violence spilling over into the hospital with the surge in gang activity--it's the stuff of movies and, increasingly, real life in urban emergency departments, even in Minnesota. The trials and tribulations of providing emergency medical care in our metropolitan areas are well documented, both in professional journals and the conventional media. It's dramatic--lives hang in the balance--and it's important to everyone, since those who will one day require emergency medical care must entrust their well-being to this system. But it's only part of the story.

Stepping Into the Right Sock.

Dressing feet is not as simple as it once was. Hundreds of types of socks-including socks for specific sports-are now available for athletic consumers. When counseling athletes dazzled by the array of options, physicians can recommend emphasizing the basics: Socks and shoes need to fit together well. Careful sock selection also can help relieve foot conditions and prevent painful blisters.

Outwitting Muscle Cramps-Is It Possible?

Muscle cramps are common among athletes who regularly work their muscles to the point of exhaustion. And some athletes will resort to anything to get rid of them.

Catastrophic Head and Neck Injuries in Amateur Hockey.

Injuries among amateur hockey players have increased during the past decade. Physicians debate contributing causes and ways to remedy the problem without altering the sport.

Precamp Physical Exams: Their Value May Be Greater Than You Think.

A precamp exam should be more than just a cursory check for heart murmurs and hernias. It should be a complete health maintenance exam-tailored to the needs of each child and to the rigors of the camp the child is going to attend.