Biomedical subjects

B de Kruijff

Publications and source records attributed to B de Kruijff.

256 records · Page 15Linked to original sources

PubMedDate not supplied

The full length of a mitochondrial presequence is required for efficient monolayer insertion and interbilayer contact formation.

The peptide specificity of both presequence-monolayer interactions and the ability of presequences to induce interbilayer contacts between large unilamellar vesicles was investigated. A range of different synthetic peptides that are documented for their mitochondrial protein import abilities were used for this purpose. Both monolayer insertion and vesicle aggregation were found to be strongly dependent on the primary structure of the studied presequence peptides. The combination of monolayer data and results of vesicle aggregation experiments leads to the overall suggestion that monolayer insertion and interbilayer contact formation are mechanistically related. For maximal effects the full length of a presequence peptide is required. The cardiolipin specificity of presequence-induced interbilayer contact formation previously reported was found to be a more general property among presequence peptides. The peptide's ability to induce vesicle-vesicle contacts seems to parallel the efficiency of its import ability into mitochondria. These results lead to an extended hypothesis on the role of presequence-induced contact site formation during the mitochondrial protein import process.

Adrenodoxin↗

PubMedDate not supplied

The specificity of glycolipid-preferredoxin interaction: requirements for membrane binding.

Preferredoxin (prefd) is a precursor protein that is imported into chloroplasts. Monolayer experiments have shown that prefd has a high affinity for monogalactosyldiglyceride (MGaIDG) isolated from chloroplasts, which contains polyunsaturated fatty acid constituents and is therefore in a liquid-expanded state, but has been found to interact also with MGaIDG with long-chain saturated fatty acids, which exist in a gel state. For an optimal interaction, the fatty acid chain length and the extent of unsaturation are also important parameters, whereas the conformation of the sugar moiety, the sugar-glycerol or glycerol-hydrocarbon chain linkages are of little influence on the pressure changes measured in monomolecular layers. Conversely, steric hindrance of a methyl group at position 3 of the sugar largely inhibits the interaction. Quantification of the interaction with radiolabelled prefd shows that only a small part of the molecule is able to penetrate MGaIDG in the gel state, whereas a nearly four-times larger part is able to penetrate MGaIDG isolated from chloroplasts. It is likely that interactions of the transit sequence of prefd with the glycolytic head group MGaIDG are involved in targeting and binding to the chloroplast membrane.

Cell Membrane↗

PubMedDate not supplied

A quantitative assay to determine the amount of signal peptidase I in E. coli and the orientation of membrane vesicles.

The number of Signal Peptidase I (SPasel) molecules per E. coli cell was determined using western blot techniques. Different strains were found to contain approximately 1000 SPasel molecules per cell during exponential growth. Based on the activity of SPasel in vitro it could be estimated that this amount is sufficient to process all translocated precursors. SPasel did not appear to be under growth phase dependent control, but was constitutively expressed. The quantitative western blot technique was also used to establish the orientation and intactness of isolated inner membrane vesicles.

Bacterial Proteins↗

PubMedDate not supplied

On the accessibility of phosphatidylglycerol to periodate in Escherichia coli.

The transverse distribution of phosphatidylglycerol (PG) across the inner membrane of Escherichia coli was studied. The oxidation of PG by periodate was used to discriminate between the PG present in the cytoplasmic and in the periplasmic leaflet of the inner membrane. Applied to large unilamellar vesicles derived of an E. coli lipid extract, the periodate method demonstrated the expected symmetrical distribution of PG over the bilayer. However, both in right-side-out and in inside-out inner membrane vesicles isolated from E. coli, as well as in intact E. coli cells, the entire pool of PG was oxidized by periodate. The oxidation reaction proceeded at such a high rate that it was impossible to determine the distribution of PG across the membrane. Apparently, periodate easily permeates through the membrane. This permeation could not be inhibited or slowed down, and it was concluded that the use of periodate as oxidizer of PG is not a suitable method to determine the transverse distribution of this phospholipid in the Gram-negative bacterium E. coli. However, periodate can be used to selectively modify the total PG pool in this organism.

Cell Membrane↗