In This Issue

579 Protease inhibitors derived from elafin and SLPI and engineered to have enhanced specificity towards neutrophil serine proteases

Marie-Louise Zani, Kévin Baranger, Nicolas Guyot, Sandrine Dallet-Choisy, and Thierry Moreau

The major serine proteases released from neutrophils including elastase, proteinase 3 and cathepsin G are well recognized to play a pivotal role in the pathogenesis of inflammatory lung diseases such as cystic fibrosis. A possible therapeutic strategy to prevent their numerous deleterious effects in the inflammatory lung is to boost the level of anti-proteases by an aerosol administration. This study represents part of an ongoing effort by these authors to develop new recombinant anti-proteases targetting efficiently all three neutrophil serine proteases at the same time, reporting the design of a series of protease inhibitors derived from natural inhibitors such as elafin or its precursor trappin-2 and SLPI. As demonstrated in this study, in addition to their extended inhibitory properties compared to wild-type inhibitors, these new inhibitors have other interesting biological properties that reinforce their potential therapeutic value.

662 Re-examining the role of Lys67 in class C β-lactamase catalysis

Yu Chen, Andrea McReynolds, and Brian K. Shoichet

Class C β-lactamases confer resistance to β-lactam antibiotics and are intensely studied. Despite this scrutiny, the deacylation mechanism continues to be debated. Lys67, in particular, lies at the center of several different mechanisms. In a conjugate base hypothesis a neutral Lys67 and Tyr150 deprotonate the deacylating water, but previous experiments on K67R mutants suggested a mainly electrostatic role. Using the β-lactamase AmpC, this was re-investigated biochemically and structurally. Both acylation and deacylation rates were substantially reduced in the K67R mutant, whereas its X-ray structure shows only slight changes. These results support a role for Lys67 in proton shuttling in deacylation, though a manifold of mechanisms may contribute, depending on the enzyme (wt or mutant) and the substrate.

670 Fast structural dynamics in reduced and oxidized cytochrome c

Weixia Liu, Jon N. Rumbley, S. Walter Englander, and A. Joshua Wand

Surprisingly modest differences in fast internal motion between oxidized (left) and reduced (right) horse cytochrome c are observed by 15N and 2H NMR relaxation. Both states of the protein are found to be unusually rigid. These results clarify several theoretical issues regarding electron transfer. Methyl groups are color coded for their amplitude of motion as represented by the symmetry axis generalized order parameter using a linear RGB color scale. Dark gray represents undetermined sites. Rendered on the crystal structures (PDB codes 1AKK and 2GIW) using VMD (Humphrey et al. 1996. VMD - Visual Molecular Dynamics. J. Molec. Graphics 14: 33–38.).

537 Structural plasticity of the phage P22 tail needle gp26 probed with Xenon gas

Adam S. Olia, Sherwood Casjens, and Gino Cingolani

The tail needle gp26 is a highly stable trimeric fiber that in bacteriophage P22 plugs the DNA exit channel and likely plays an important role in the ejection of the phage genome into the host. The 1.98Å resolution crystal structure of gp26 bound to xenon gas presented in this report led to the identification of seven small cavities occupied by xenon atoms. These small internal cavities confer flexibility to the C-terminal tip of the needle, which allows for relative motion of the tip with respect to the helical core, thus acting as a probe to scan the bacterial surface, in search of a penetration site.