Detergent activation of the ATPase activity of chloroplast coupling factor 1

The activation of the ATPase activity of coupling factor 1 (CF1) from chloroplasts by several detergents was studied. Further evidence that detergent micelles are important in the activation of Ca2+-ATPase was obtained. Maximal activation of CA2+-ATPase was achieved with short-chain alkyl-beta-D-glucopyranoside (alkylglucosides) detergents. Treatment of CF1 with hexylglucoside or heptylglucoside followed by hydroxylapatite chromatography caused nearly total removal of the epsilon subunit of the enzyme, whereas treatment with decylglucoside caused less ATPase activation and less loss of the epsilon subunit. The ATPase activity of detergent-activated CF1 was inhibited by purified epsilon subunit. Detergents that form small micelles appear to be most effective in removing the epsilon subunit and in activating the Ca2+-ATPase of CF1. When present during assay, the alkylglucosides also induce a Mg2+-ATPase activity in CF1. Octyl- and nonylglucoside are most effective in promoting this reaction. If, however, CF1 deficient in the epsilon subunit was used, even decylglucoside elicited rapid Mg2+-ATPase hydrolysis. It is concluded that removal of the epsilon subunit, although necessary for the expression of Mg2+-ATPase, is not sufficient. The detergents that cause maximal displacement of the epsilon subunit are less effective in inducing Mg2+-ATPase activity. The selective removal of subunits from CF1 by specific detergents points to potential problems with the use of these detergents in the solubilization of oligomeric membrane proteins.

Nucleotide sequence of the lspA gene, the structural gene for lipoprotein signal peptidase of Escherichia coli

The nucleotide sequence of the lspA gene coding for lipoprotein signal peptidase of Escherichia coli was determined and the amino acid sequence of the peptidase was deduced from it. The molecular mass and amino acid composition of the predicted lipoprotein signal peptidase were consistent with those of the signal peptidase purified from cells harboring the lspA gene-carrying plasmid. The peptidase most probably has no cleavable signal peptide. The lspA gene was preceded by the ileS gene coding for isoleucyl-tRNA synthetase and the tandem termination codons of the ileS gene overlapped with the initiation codon of the lspA gene.

Mechanism of localization of major outer membrane lipoprotein in Escherichia coli. Studies with the OmpF-lipoprotein hybrid protein

A chimera gene consisting of the ompF promoter, the coding regions for the signal peptide and the NH2-terminal 11 amino acid residues of outer membrane OmpF protein, and the coding region for the major outer membrane lipoprotein devoid of the NH2-terminal 7 amino acid residues was constructed. Escherichia coli carrying the cloned chimera gene produced a hybrid protein with the predicted chemical structure. The protein was localized in the periplasmic space with an interaction with the peptidoglycan layer. These results indicate that the hybrid protein was expressed, secreted across the cytoplasmic membrane, and processed for the signal peptide normally. The hybrid protein, however, was not incorporated into the outer membrane, suggesting the importance of the lipid domain in the assembly of the lipoprotein into the outer membrane. Although a larger part of the protein was extractable with sodium dodecyl sulfate, a part of the hybrid protein was covalently bound to the peptidoglycan layer as the lipoprotein is. Upon treatment with lysozyme of the envelope the hybrid protein became water soluble. The solubilized protein most probably existed as a trimer. These results most likely suggest that the major lipoprotein exists as a trimer in the periplasmic space with interactions with the peptidoglycan layer through the protein domain on one side and with the outer membrane through the lipid domain on the other side.

Roles of lipopolysaccharide and outer membrane protein OmpC of Escherichia coli K-12 in the receptor function for bacteriophage T4

The roles of lipopolysaccharide and OmpC, a major outer membrane protein, in the receptor function for bacteriophage T4 were studied by using Escherichia coli K-12 strains having mutations in the ompC gene or in genes controlling different stages of lipopolysaccharide synthesis. The receptor activity for T4 was monitored by (i) T4 sensitivity of intact cells, (ii) phage inactivation activity of cell envelopes, and (iii) phage inactivation activity of specimens reconstituted from purified OmpC and lipopolysaccharide. It was found that (i) in the presence of the OmpC protein, the essential region of the lipopolysaccharide for the receptor activity was the core-lipid A region that includes the heptose region, whereas the glucose region was not necessarily required for the receptor function; (ii) the OmpC protein was not required at all when the distal end of the lipopolysaccharide was removed to expose a glucose residue at the distal end; and (iii) when cells lacked both the OmpC protein and the glucose region, they became extremely resistant to T4. Based on these findings, the roles of the OmpC protein and lipopolysaccharide in T4 infection are discussed.

Role of lipopolysaccharide in the receptor function for bacteriophage TuIb in Escherichia coli

Bacteriophage TuIb required lipopolysaccharide in addition to the OmpC trimer as a receptor component. Both the fatty acid and polysaccharide regions of lipopolysaccharide were shown to participate in the receptor function. The roles of lipopolysaccharide and outer membrane proteins in the receptor function for T-even type bacteriophages are discussed.