Structural insights into the regulatory mechanism of the Pseudomonas aeruginosa YfiBNR system

YfiBNR is a recently identified bis-(3'-5')-cyclic dimeric GMP (c-di-GMP) signaling system in opportunistic pathogens. It is a key regulator of biofilm formation, which is correlated with prolonged persistence of infection and antibiotic drug resistance. In response to cell stress, YfiB in the outer membrane can sequester the periplasmic protein YfiR, releasing its inhibition of YfiN on the inner membrane and thus provoking the diguanylate cyclase activity of YfiN to induce c-di-GMP production. However, the detailed regulatory mechanism remains elusive. Here, we report the crystal structures of YfiB alone and of an active mutant YfiB(L43P) complexed with YfiR with 2:2 stoichiometry. Structural analyses revealed that in contrast to the compact conformation of the dimeric YfiB alone, YfiB(L43P) adopts a stretched conformation allowing activated YfiB to penetrate the peptidoglycan (PG) layer and access YfiR. YfiB(L43P) shows a more compact PG-binding pocket and much higher PG binding affinity than wild-type YfiB, suggesting a tight correlation between PG binding and YfiB activation. In addition, our crystallographic analyses revealed that YfiR binds Vitamin B6 (VB6) or L-Trp at a YfiB-binding site and that both VB6 and L-Trp are able to reduce YfiB(L43P)-induced biofilm formation. Based on the structural and biochemical data, we propose an updated regulatory model of the YfiBNR system.

Toxicity of acrylamide on male reproduction / 中华男科学杂志

Acrylamide is a common chemical material, extensively used in industry and scientific experiments. Recently, it has been reported that starchy food cooked at high temperature can produce acrylamide. Acrylamide monomer has several toxic effects and the extensive concern for its toxicity has arisen with the finding of acrylamide formation in some processed foods. Researches have shown that acrylamide monomer can cause reproductive toxicity, including toxic effects on male reproductive behavior, male reproductive endocrine function and spermatogenesis. The mechanisms may include the effects of acrylamide on Leydig cells, the formation of motor protein/ chromosomal/DNA alkylation and damage by oxidative stress.

Subchronic exposure to acrylamide affects reproduction and testis endocrine function of rats / 中华男科学杂志

<p><b>OBJECTIVE</b>To explore the effect of subchronic exposure to acrylamide on the reproduction and testis endocrine function of rats.</p><p><b>METHODS</b>Forty healthy adult male SD rats were randomly divided into 4 groups of equal number, exposed to acrylamide at the dose of 0, 4, 10 and 18 mg/(kg x d) respectively for 9 weeks, and then subjected to the determination of the hindlimb landing foot splay, sperm vitality and morphology, the activities of acid phosphatase (ACP) and alkaline phosphatase (ALP) in the testis homogenate, and the levels of testosterone (T) and estradiol (E2) in the serum and testis homogenate. Based on the primary Leydig cell culture models exposed to acrylamide of 0, 0.1, 0.75, 4 and 8 mmol/L, the activity of Leydig cells was measured by the CCK-8 method.</p><p><b>RESULTS</b>Following acrylamide exposure, the hindlimb landing foot splay increased markedly with dose increase (P < 0.01). The rates of sperm vitality were (6.86 +/- 5.46)%, (65.43 +/- 5.16)%, (60.86 +/- 4.26)% and (46.86 +/- 2.73)% in the exposed groups, significantly lower than in the control (P < 0.01); the rates of abnormal sperm were (39.00 +/- 10.95)%, (35.43 +/- 7.54)%, (45.71 +/- 13.28)% and (56.71 +/- 17.01)%, significantly increased in the 10 and 18 mg/(kg x d) groups (P < 0.05); ACP activities were (82.93 +/- 11.05), (73.52 +/- 8.77), (77.67 +/- 3.04) and (68.56 +/- 3.09) U/g prot, showing a decreasing tendency, while ALP activities were (0.96 +/- 0.15), (1.07 +/- 0.22), (1.12 +/- 0.22) and (0.74 +/- 0.10) U/g prot, displaying a tendency of first increasing and then decreasing. Both ACP and ALP activities were inhibited significantly in the 18 mg/(kg x d) group as compared with the control (P < 0.05). A marked reduction was noted in T levels in the serum, (13.44 +/- 4.76), (7.69 +/- 3.84), (5.23 +/- 1.42) and (1.36 +/- 0.86) ng/ml, as well as in the testis homogenate, (4.95 +/- 1.64), (3.01 +/- 0.76), (2.44 +/- 0.91) and (0.85 +/- 0.49) ng/mg prot, (P < 0.01), but no significant changes were observed in 17beta-E2 levels. After 24 hours exposure to acrylamide, the optical densities were 0.82 +/- 0.06, 0.56 +/- 0.07, 0.44 +/- 0.06, 0.26 +/- 0.03 and 0.45 +/- 0.21, showing an evident inhibition of the activity of Leydig cells at the dose of 0.1, 0.75, 4 and 8 mmol/L (P < 0.01).</p><p><b>CONCLUSION</b>Subchronic exposure to acrylamide could affect the normal development of sperm, cause changes of the activity of some enzymes in the testis and significantly influence hindlimb motor coordination. Acrylamide directly damages Leydig cells and affects the endocrine function of the testis.</p>