A 15 kDa proteolipid found in mediatophore preparations from Torpedo electric organ presents high sequence homology with the bovine chromaffin granule protonophore

Upon SDS PAGE of isolated mediatophore, an acetylcholine-translocating protein, a doublet at 15 kDa was identified. Amino acid sequencing after CNBr cleavage gave a 17 residue-long peptide completely homologous with a sequence of the proton-translocating proteolipid from bovine chromaffin granules. A 51-mer oligodeoxynucleotide corresponding to this sequence was used to screen a library of electric lobe cDNAs constructed in lambda Zap II. A positive recombinant clone was isolated and found to encode the complete sequence of a 15.5 kDa protein highly homologous to the bovine chromaffin or yeast vacuolar ATPase proteolipid. In vitro translation of sense RNA transcripts of the clone indeed yielded a single 15 kDa proteolipid. Northern blot analysis showed that the 1.3 kb mRNA encoding this protein is significantly expressed in nervous tissues but not in electric organ or liver of Torpedo marmorata.

Posttranslational glutamylation of alpha-tubulin

The high degree of tubulin heterogeneity in neurons is controlled mainly at the posttranslational level. Several variants of alpha-tubulin can be posttranslationally labeled after incubation of cells with [3H]acetate or [3H]glutamate. Peptides carrying the radioactive moiety were purified by high-performance liquid chromatography. Amino acid analysis, Edman degradation sequencing, and mass spectrometric analysis of these peptides led to the characterization of a posttranslational modification consisting of the successive addition of glutamyl units on the gamma-carboxyl group of a glutamate residue (Glu445). This modification, localized within a region of alpha-tubulin that is important in the interactions of tubulin with microtubule-associated proteins and calcium, could play a role in regulating microtubule dynamics.

On the use of polyethylenimine as a carrier for protein sequencing: comparison with polybrene

In the gas-liquid phase automated protein sequencer, polyethylenimine was used as a hydrophilic entrapping polymer. Glass fiber filters soaked in 0.3% solution of polyethylenimine were used. Sperm whale myoglobin, beta-lactoglobulin, and several peptides with basic or acidic pI were sequenced. Loads from 20 to 26,000 pmol were tested. Initial and repetitive yields compare favorably to those obtained with polybrene-coated glass fiber filters. Recovery of individual amino acids shows that none gave a particularly low yield, in contrast with the low recovery of Arg, Trp, His, Glu, and Asp when polybrene was used. The usual artefacts were greatly diminished and even disappeared as in the case of N,N'-diphenylurea. Substitution of polyethylenimine for polybrene sped up the analysis because the precycling employed to condition polybrene-coated glass fiber filters was no longer necessary. In conclusion polyethylenimine appears superior to polybrene for sequencing protein and peptides.