Isolation of a secY homologue from Bacillus subtilis: evidence for a common protein export pathway in eubacteria

Abstract

Genetic and biochemical studies have shown that the product of the Escherichia coli secY gene is an integral membrane protein with a central role in protein secretion. We found the Bacillus subtilis secY homologue within the spc-alpha ribosomal protein operon at the same position occupied by E. coli secY. B. subtilis secY coded for a hypothetical product 41% identical to E. coli SecY, a protein thought to contain 10 membrane-spanning segments and 11 hydrophilic regions, six of which are exposed to the cytoplasm and five to the periplasm. We predicted similar segments in B. subtilis SecY, and the primary sequences of the second and third cytoplasmic regions and the first, second, fourth, fifth, seventh, and tenth membrane segments were particularly conserved, sharing greater than 50% identity with E. coli SecY. We propose that the conserved cytoplasmic regions interact with similar cytoplasmic secretion factors in both organisms and that the conserved membrane-spanning segments actively participate in protein export. Our results suggest that despite the evolutionary differences reflected in cell wall architecture, Gram-negative and Gram-positive bacteria possess a similar protein export apparatus.

Characterisation of a chloroplast‐encoded sec Y homologue and atpH from a chromophytic alga Evidence for a novel chloroplast genome organisation

“…The five SecY protein sequences are approximately 50% conserved, with regions of honaology confined to ten hydrophobic regions and several charged regions. These domains correspond to the ten putative hydrophobic, membrane-spanning regions (MSR) and four cytosolicaily exposed charged loops consistent with the structure of other SecY proteins [6,8,9,17]. However, P. lutherii SecY shows considerable variation at both termini, in particular at the amino terminus, which contains an additional 7 and 39 amino acid re.~idues in the E. coil and C. paradoxa SecY proteins respectively.…”

“…These features are common to the translocation process across the eukaryotic rough eitdoplasmic reticulure [24]. Suh et al (1990) [8] suggest that signal peptide recognition proteins [25,26] and the soluble cytoplasmic SecA proteins [27,28] are likely candidates for interaction with SecY in order to facilitate bacterial protein translocation. A chloroplast-encoded gene which predicts a protein related to bacterial SecA [27,28] is also present in P. lutherii (Scaramuzzi, PhD Thesis, 1991).…”

“…It is presumed that the remainder have been lost or transferred to the nucleus. Among these is sec Y, of the spc operon the product of which is involved in prokaryotic protein translocation [8]. We report here the nucleotide sequence of two chloroplastencoded genes, seeY and atpH, from the chromophytic alga, Pavlova lutherii and show that they are linked on the chloroplast genome but positioned independently of the rp cluster.…”

“…Some genes involved in protein translocation have also been retained on the chloroplast genome of eukaryotic algae outside of the chlorophyta [4][5][6]. The sec Y gone is found in both Escherichia cell [7] and Bacillus subtilis [8] where it forms part of the spc operon of the ribosomal protein (rp) gone cluster and in Cyanophora paradoxa [9] where it is located immediately adjacent to the final gone of this operon. Recently, a chloroplast-encoded sec Y homologue from a cryptophytic algae has also been located within the spc operon [6].…”

Biochemical analysis of the biogenesis and function of the Escherichia coli export factor SecY

“…It is essential for the export of periplasmic and outer-membrane proteins of Escherichia coli since mutations in the sec Y gene result in temperature-sensitive export defects, as shown both in vivo (Ito et al, 1983Shiba et al, 1984) and in vitro (Fandl and Tai, 1987;Baba et al, 1990). Homologues ofsecY have also been found in Bacillus subtilis (Suh et al, 1990), Mycoplasma capricolwn (Ohkubo et al, 1987) and Lactococcus lactis (Koivula et al, 1991). Distinct mutations in E. coli secY (designated prlA) suppress the export defects of various signal-sequence mutations (Emr et al, 1981 ;Emr and Bassford, 1982;Stader et al, 1986;Sako and Iino, 1988;Puziss et al, 1992), suggesting a, presumably transient, recognition by SecY of exported proteins via their signal sequences.…”