Molecular biology and bacterial secondary transporters☆

Evidence for Intraprotein Charge Transfer during the Transport Activity of the Melibiose Permease from Escherichia Coli

“…Biochemical and spectroscopic evidence support the earlier suggestion that some discrete steps of MelB cycling involve conformational transitions of the transporter (21). This includes cooperative protection against proteolysis of the highly charged cytoplasmic loop connecting helices IV and V (loop 4-5) of MelB (14) by MelB substrates.…”

Evidence for Intraprotein Charge Transfer during the Transport Activity of the Melibiose Permease from Escherichia Coli

“…Biochemical and spectroscopic evidence support the earlier suggestion that some discrete steps of MelB cycling involve conformational transitions of the transporter (21). This includes cooperative protection against proteolysis of the highly charged cytoplasmic loop connecting helices IV and V (loop 4-5) of MelB (14) by MelB substrates.…”

Membrane insertion of uracil permease, a polytopic yeast plasma membrane protein.

“…The uracil permease produced by in vitro synthesis or detected after in vivo labeling and immunoprecipitation appeared as a diffuse band on denaturing polyacrylamide gels, with an apparent size of 50 to 55 kDa, i.e., 15 kDa smaller than that deduced from nucleotide sequence data. This discrepancy, which did not result from artifactual proteolysis, has also been seen with other highly hydrophobic proteins, including several bacterial permeases (11,22) and S. cerevisiae a-factor receptor (4). It has generally been attributed to the binding of high concentrations of SDS (14,29) or incomplete denaturation by SDS (41), which could also result in microheterogeneity, leading to the diffuse signal on the gel.…”

Evidence for Intraprotein Charge Transfer during the Transport Activity of the Melibiose Permease from Escherichia Coli

“…Biochemical and spectroscopic evidence support the earlier suggestion that some discrete steps of MelB cycling involve conformational transitions of the transporter (21). This includes cooperative protection against proteolysis of the highly charged cytoplasmic loop connecting helices IV and V (loop 4-5) of MelB (14) by MelB substrates.…”

Membrane insertion of uracil permease, a polytopic yeast plasma membrane protein.

“…The uracil permease produced by in vitro synthesis or detected after in vivo labeling and immunoprecipitation appeared as a diffuse band on denaturing polyacrylamide gels, with an apparent size of 50 to 55 kDa, i.e., 15 kDa smaller than that deduced from nucleotide sequence data. This discrepancy, which did not result from artifactual proteolysis, has also been seen with other highly hydrophobic proteins, including several bacterial permeases (11,22) and S. cerevisiae a-factor receptor (4). It has generally been attributed to the binding of high concentrations of SDS (14,29) or incomplete denaturation by SDS (41), which could also result in microheterogeneity, leading to the diffuse signal on the gel.…”

Evidence for Intraprotein Charge Transfer during the Transport Activity of the Melibiose Permease from Escherichia Coli

“…Biochemical and spectroscopic evidence support the earlier suggestion that some discrete steps of MelB cycling involve conformational transitions of the transporter (21). This includes cooperative protection against proteolysis of the highly charged cytoplasmic loop connecting helices IV and V (loop 4-5) of MelB (14) by MelB substrates.…”

Membrane insertion of uracil permease, a polytopic yeast plasma membrane protein.

“…The uracil permease produced by in vitro synthesis or detected after in vivo labeling and immunoprecipitation appeared as a diffuse band on denaturing polyacrylamide gels, with an apparent size of 50 to 55 kDa, i.e., 15 kDa smaller than that deduced from nucleotide sequence data. This discrepancy, which did not result from artifactual proteolysis, has also been seen with other highly hydrophobic proteins, including several bacterial permeases (11,22) and S. cerevisiae a-factor receptor (4). It has generally been attributed to the binding of high concentrations of SDS (14,29) or incomplete denaturation by SDS (41), which could also result in microheterogeneity, leading to the diffuse signal on the gel.…”