Crystal structure of Yersinia pestis virulence factor YfeA reveals two polyspecific metal-binding sites.

Gram-negative bacteria use siderophores, outer membrane receptors, inner membrane transporters and substrate-binding proteins (SBPs) to transport transition metals through the periplasm. The SBPs share a similar protein fold that has undergone significant structural evolution to communicate with a variety of differentially regulated transporters in the cell. In Yersinia pestis, the causative agent of plague, YfeA (YPO2439, y1897), an SBP, is important for full virulence during mammalian infection. To better understand the role of YfeA in infection, crystal structures were determined under several environmental conditions with respect to transition-metal levels. Energy-dispersive X-ray spectroscopy and anomalous X-ray scattering data show that YfeA is polyspecific and can alter its substrate specificity. In minimal-media experiments, YfeA crystals grown after iron supplementation showed a threefold increase in iron fluorescence emission over the iron fluorescence emission from YfeA crystals grown from nutrient-rich conditions, and YfeA crystals grown after manganese supplementation during overexpression showed a fivefold increase in manganese fluorescence emission over the manganese fluorescence emission from YfeA crystals grown from nutrient-rich conditions. In all experiments, the YfeA crystals produced the strongest fluorescence emission from zinc and could not be manipulated otherwise. Additionally, this report documents the discovery of a novel surface metal-binding site that prefers to chelate zinc but can also bind manganese. Flexibility across YfeA crystal forms in three loops and a helix near the buried metal-binding site suggest that a structural rearrangement is required for metal loading and unloading.

The effect of mannan oligosaccharide supplementation on body weight gain and fat accrual in C57Bl/6J mice.

The prevalence of obesity in industrialized societies has become markedly elevated. In contrast, model organism research shows that reducing caloric intake below ad libitum levels provides many health and longevity benefits. Despite these benefits, few people are willing and able to reduce caloric intake over prolonged periods. Prior research suggests that mannooligosaccharide (MOS or mannan) supplementation can increase lifespan of some livestock and in rodents can reduce visceral fat without reducing caloric intake. Hence, we tested the effect of MOS supplementation as a possible calorie restriction (CR) mimetic (CRM) in mice. C57Bl/6J male mice were fed a high-fat "western" type diet with or without 1% MOS (by weight) supplementation (n = 24/group) from 8 to 20 weeks of age. Animals were housed individually and provided 95% of ad libitum food intake throughout the study. Body weight was measured weekly and body composition (lean and fat mass) measured noninvasively every 3 weeks. Individual fat depot weights were acquired by dissection at study completion. Supplementation of a high-fat diet with 1% MOS tended to reduce total food intake (mean +/- s.d.; control (CON): 293.69 +/- 10.53 g, MOS: 288.10 +/- 11.82 g; P = 0.09) during the study. Moreover, MOS supplementation had no significant effect on final body weight (CON: 25.21 +/- 2.31 g, MOS: 25.28 +/- 1.49 g; P = 0.91), total fat (CON: 4.72 +/- 0.90 g, MOS: 4.82 +/- 0.83 g; P = 0.69), or visceral fat (CON: 1.048 +/- 0.276 g, MOS: 1.004 +/- 0.247 g; P = 0.57). Contrary to previous research, MOS supplementation had no discernable effect on body weight gain or composition during this 12-week study, challenging the potential use of MOS as a CRM or body composition enhancer.