The molecular basis of polysaccharide cleavage by lytic polysaccharide monooxygenases.

Lytic polysaccharide monooxygenases (LPMOs) are copper-containing enzymes that oxidatively break down recalcitrant polysaccharides such as cellulose and chitin. Since their discovery, LPMOs have become integral factors in the industrial utilization of biomass, especially in the sustainable generation of cellulosic bioethanol. We report here a structural determination of an LPMO-oligosaccharide complex, yielding detailed insights into the mechanism of action of these enzymes. Using a combination of structure and electron paramagnetic resonance spectroscopy, we reveal the means by which LPMOs interact with saccharide substrates. We further uncover electronic and structural features of the enzyme active site, showing how LPMOs orchestrate the reaction of oxygen with polysaccharide chains.We thank K. Rasmussen and R.M. Borup for experimental assistance, and MAXLAB, Sweden and the European Synchrotron Radiation Facility (ESRF), France, for synchrotron beam time and assistance. This work was supported by the UK Biotechnology and Biological Sciences Research Council (grant numbers BB/L000423 to P.D., G.J.D. and P.H.W., and BB/L021633/1 to G.J.D. and P.H.W.), Agence Française de l'Environnement et de la Maîtrise de l'Energie (grant number 1201C102 to B.H.), the Danish Council for Strategic Research (grant numbers 12-134923 to L.L.L. and 12-134922 to K.S.J.). Travel to synchrotrons was supported by the Danish Ministry of Higher Education and Science through the Instrument Center DANSCATT and the European Community's Seventh Framework Programme (FP7/2007-2013) under BioStruct-X (grant agreement 283570). L.M., S.F., S.C. and H.D. were supported by Institut de Chimie Moléculaire de Grenoble FR 2607, LabEx ARCANE (ANR-11-LABX-0003-01), the PolyNat Carnot Institute and the French Agence Nationale de la Recherche (PNRB2005-11).This is the author accepted manuscript. The final version is available from Nature Publishing Group via http://dx.doi.org/10.1038/nchembio.202

Risk reduction practices in men who have sex with men in Switzerland: serosorting, strategic positioning, and withdrawal before ejaculation.

The aim of this study was to identify predictors of intentional use of the HIV risk reduction practices of serosorting, strategic positioning, and withdrawal before ejaculation during unprotected anal intercourse (UAI) with casual partners. A cross-sectional survey pertaining to the Swiss HIV behavioral surveillance system, using an anonymous self-administered questionnaire, was conducted in 2007 in a self-selected sample of men having sex with other men (MSM). Analysis was restricted to participants with UAI with casual partner(s) (N = 410). Logistic regression was used to estimate factors associated with intentional use of serosorting, strategic positioning, and withdrawal before ejaculation. In the previous 12 months, 71% of participants reported having UAI with a casual partner of different or unknown HIV-status. Of these, 47% reported practicing withdrawal, 38% serosorting, and 25% strategic positioning. In the 319 participants with known HIV-status, serosorting was associated with frequent Internet use to find partners (OR = 2.32), STI (OR = 2.07), and HIV testing in the past 12 months (OR = 1.81). Strategic positioning was associated with HIV-status (OR = 0.13) and having UAI with a partner of different or unknown HIV-status (OR = 3.57). Withdrawal was more frequently practiced by HIV-negative participants or participants reporting high numbers of sexual partners (OR = 2.48) and having UAI with a partner of unknown or different serostatus (OR = 2.08). Risk reduction practices are widely used by MSM, each practice having its own specificities. Further research is needed to determine the contextual factors surrounding harm reduction practices, particularly the strategic or opportunistic nature of their use