Wheel of Life, Wheel of Death: A Mechanistic Insight into Signaling by STAND Proteins.

The signal transduction ATPases with numerous domains (STAND) represent a newly recognized class of widespread, sophisticated ATPases that are related to the AAA+ proteins and that function as signaling hubs. These proteins control diverse biological processes in bacteria and eukaryotes, including gene expression, apoptosis, and innate immunity responses. They function as tightly regulated switches, with the off and on positions corresponding to a long-lived monomeric, ADP-bound form and a multimeric, ATP-bound form, respectively.

Identification of essential residues in apolipoprotein N-acyl transferase, a member of the CN hydrolase family.

Apolipoprotein N-acyl transferase (Lnt) is an essential membrane-bound protein involved in lipid modification of all lipoproteins in gram-negative bacteria. Essential residues in Lnt of Escherichia coli were identified by using site-directed mutagenesis and an in vivo complementation assay. Based on sequence conservation and known protein structures, we predict a model for Lnt, which is a member of the CN hydrolase family.

Direct visualization of red fluorescent lipoproteins indicates conservation of the membrane sorting rules in the family Enterobacteriaceae.

Chimeras created by fusing the monomeric red fluorescent protein (RFP) to a bacterial lipoprotein signal peptide (lipoRFPs) were visualized in the cell envelope by epifluorescence microscopy. Plasmolysis of the bacteria separated the inner and outer membranes, allowing the specific subcellular localization of lipoRFPs to be determined in situ. When equipped with the canonical inner membrane lipoprotein retention signal CDSR, lipoRFP was located in the inner membrane in Escherichia coli, whereas the outer membrane sorting signal CSSR caused lipoRFP to localize to the outer membrane.

Depletion of apolipoprotein N-acyltransferase causes mislocalization of outer membrane lipoproteins in Escherichia coli.

Lipoproteins in Gram-negative Enterobacteriaceae carry three fatty acids on the N-terminal cysteine residue, two as a diacylglyceride and one through an N-linkage following signal peptide cleavage. Most lipoproteins are anchored in the outer membrane, facing the periplasm, but some lipoproteins remain in the plasma membrane, depending on the amino acid at position +2, immediately after the fatty-acylated cysteine. In vitro, the last step in lipoprotein maturation, N-acylation of apolipoproteins by the plasma membrane apolipoprotein N-acyltransferase (Lnt), is necessary for efficient recognition of outer membrane lipoproteins by the Lol system, which transports them from the plasma to the outer membrane (Fukuda, A.

Type II protein secretion and its relationship to bacterial type IV pili and archaeal flagella.

Homologues of the protein constituents of the Klebsiella pneumoniae (Klebsiella oxytoca) type II secreton (T2S), the Pseudomonas aeruginosa type IV pilus/fimbrium biogenesis machinery (T4P) and the Methanococcus voltae flagellum biogenesis machinery (Fla) have been identified. Known constituents of these systems include (1). a major prepilin (preflagellin), (2).