PqqF inhibits T6SS secretion by decreasing the pH in Serratia marcescens FS14.

Pyrroloquinoline quinone (PQQ) is a redox cofactor with numerous important physiological functions, and the type VI secretion system (T6SS) is commonly found in Gram-negative bacteria and plays important roles in physiological metabolism of the bacteria. In this study, we found that the deletion of pqqF enhanced the secretion of Hcp-1 in Serratia marcesens FS14 in M9 medium. Transcriptional analysis showed that the deletion of pqqF almost had no effect on the expression of T6SS-1.

Crystal structures of PigF, an -methyltransferase involved in the prodigiosin synthetic pathway, reveal an induced-fit substrate-recognition mechanism.

Prodigiosin, a red linear tripyrrole pigment, is a typical secondary metabolite with numerous biological functions, such as anticancer, antibacterial and immunosuppressant activities, and is synthesized through a bifurcated biosynthesis pathway from 4-methoxy-2,2'-bipyrrole-5-carbaldehyde (MBC) and 2-methyl-3--amylpyrrole (MAP). The last step in the biosynthetic pathway of MBC is catalysed by PigF, which transfers a methyl group to 4-hydroxy-2,20-bipyrrole-5-carbaldehyde (HBC) to form the final product MBC. However, the catalytic mechanism of PigF is still elusive.

Crystal structures of TTHA1265 and TTHA1264/TTHA1265 complex reveal an intrinsic heterodimeric assembly.

Zinc peptidase M16 family members are widely distributed in most prokaryotic and eukaryotic organisms. M16 family has been divided into three subfamilies, M16A, M16B and M16C, based on sequence alignments and subunit connectivity. TTHA1264, an M16B protein found in Thermus thermophiles HB8, possesses an HXXEH motif essential for Zn binding and catalytic activity.

Two component system CpxR/A regulates the prodigiosin biosynthesis by negative control in Serratia marcescens FS14.

Prodigiosin is a tripyrrole red secondary metabolite synthesized by many microorganisms, including Serratia marcescens. In this study, we found that the deletion of the gene of sensor kinase CpxA dramatically decreased the prodigiosin production, while the deletion of the gene of the response regulator CpxR or both genes of CpxRA has no effect on prodigiosin production, the kinase function of CpxA is not essential for its regulation on prodigiosin production while the phosphorylation site of CpxR is required. We further demonstrated that the CpxA regulates the prodigiosin biosynthesis at the transcriptional level and the phosphatase activity of CpxA plays vital roles in the regulation of prodigiosin biosynthesis.

Crystal structure of mature myroilysin and implication for its activation mechanism.

Myroilysin is a novel bacterial member of M12A metalloproteases family with an uncommon "cysteine switch" activation mechanism and a unique "cap" structure. However, activation of pro-myroilysin is elusive. Here, mature myroilysin was obtained for structure determination by treating pro-myroilysin with trypsin.

Crystal structure of the periplasmic domain of TssL, a key membrane component of Type VI secretion system.

Type VI secretion system (T6SS), as a macromolecular system, is commonly found in Gram-negative bacteria and responsible for exporting effectors. T6SS consists of 13 core proteins. TssL is a component of the membrane complex and plays a pivotal role in T6SS.

Crystal structure of the sensor domain of BaeS from Serratia marcescens FS14.

The sensor histidine kinases of two-component signal-transduction systems (TCSs) are essential for bacteria to adapt to variable environmental conditions. The two-component regulatory system BaeS/R increases multidrug and metal resistance in Salmonella and Escherichia coli. In this study, we report the X-ray structure of the periplasmic sensor domain of BaeS from Serratia marcescens FS14.