The <i>Streptomyces lividans</i> Cytoplasmic Signal Recognition Particle Receptor FtsY Is Involved in Protein Secretion

Abstract

The bacterial version of the mammalian signal recognition particle (SRP) and its receptor α-subunit (FtsY) is well conserved and essential to all known bacteria. In Gram-negative bacteria, the SRP pathway mediates a co-translational targeting of most inner membrane proteins. Additionally, in Streptomyces lividans, a Gram-positive bacterium, SRP also targets secretory proteins to the translocon. The role of S. lividans FtsY has been assessed in this work. Co-immunoprecipitation studies confirmed that FtsY is associated with the S. lividans SRP in the cytoplasm and that this complex also co-immunoprecipitated with pre-agarase, suggesting that the SRP receptor is involved in SRP-mediated targeting of secretory proteins in S. lividans. Furthermore, the SRP remains attached for the most part to the cellular membrane when the cleavage of pre-secretory proteins is severely reduced in a strain lacking the gene coding for the major type-I signal peptidase.

Summing up particular features of protein secretion in Streptomyces lividans

“…This proteomic analysis of the S. lividans secretome confirmed the differences in extracellular protein patterns between S. lividans TK21 and the different sip mutant strains, revealing a severe reduction in the accumulation of extracellular proteins in the sipY mutant compared to that of the remaining sip mutants, and additionally confirming the major role played by the SipY protein in secretion (Palacín et al 2002). The SipY mutant also experiences intracellular retention of a model secretory protein (Palomino and Mellado 2005), consequently affecting the intracellular distribution of the secretion pathway components, blocking the translocon temporarily and triggering the accumulation of the model pre-protein at the membrane.…”

“…The use of an S. lividans strain lacking the gene coding for the major type I signal peptidase has permitted finding evidence of an in vivo interaction of the FtsY receptor with the SRP, as well as FtsY involvement in targeting secretory proteins to the membrane via the existence of a soluble FtsY, which acts as a functional cytoplasmic receptor for the SRP (Palomino and Mellado 2005). Inactivation of the eukaryotic translocon causes accumulation of membrane-bound SRP-RNC and its receptor, by diminishing the transfer of the signal peptide from the SRP54 to the vacant translocon complexes (Song et al 2000).…”

Functional substitution of the transient membrane-anchor domain inEscherichia coliFtsY with an N-terminal hydrophobic segment ofStreptomyces lividansFtsY

“…Although the FtsY protein in S. coelicolor is estimated to be a membrane‐associated protein because it harbors an N‐terminal hydrophobic segment (Bibi et al , 2001), a large proportion of S. lividans FtsY is found in the cytoplasm (Palomino & Mellado, 2005). A mechanism that retains S. lividans FtsY in the cytoplasm must be presumed to explain this inconsistency.…”

The Cellular Mechanisms that Ensure an Efficient Secretion in Streptomyces

“…Therefore, it is helping detect the SRP ability to escort the pre-protein to the translocase complex [ 33 ]. This SipY deficiency also favored detecting an in vivo interaction of the SRP with a soluble form of FtsY, which acts as a functional cytoplasmic SRP receptor [ 36 ].…”