Membrane insertion sequence

Little is known about the L-arabinofuranosyl transfer machinery. A gene in the genome of A. thaliana has been identified as a membrane-bound arabino-furanosyl transferase by its membrane-insertion sequence and the fact that mutants in the gene led to expression of mRNA, but phenotypes that were nonetheless defective in arabinan side-chains of their pectin. Attempts to use UDP-a-L-arabinopyranose as arabinofuranose donor in crude extracts, presumably in an attempt to uncover any mutase similar to UDP galactopyranose mutase (see Section 5.12.4), merely resulted in the incorporation of pyranose units into the arabinan. However, an enzyme using this donor has been shown to add the terminal arabinopyranosyl residue to the 3-position of the terminal arabinose of the 1,5-arabininan of rhamnogalacturonan 1. [By contrast, the o-arabinofuranosyl transfer machinery that produces the... 

Structural and functional studies of a synthetic peptide that mimics a proposed membrane inserting segment of a Bacillus thuringiensis delta-endotoxin have been conducted. An NMR study of a methanol solution of a synthetic 31-mer peptide corresponding to the sequence of a putative pore-forming segment of the CrylA(c) toxin showed that the peptide exists as an a-helix. Hie peptide forms discrete, characterizable channels in planar lipid bilayers. It is possible that this helix is a component of the transmembrane pore formed by Bacillus thuringiensis delta-endotoxins in vivo. 

Zhang, J.T., Sequence requirements for membrane assembly of polytopic membrane proteins molecular dissection of the membrane insertion process and topogenesis of the human MDR3 P-glycoprotein, Mol Biol Cell 7 (1996) 1709-1721. 

J Calamia and C. Manoil, Lac permease of Escherichia coU Topology and sequence elements promoting membrane insertion, Proc. Natl. Acad. Sci. USA 87, 4937-4941 (1990). 

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