5nco | pdb_00005nco
Quaternary complex between SRP, SR, and SecYEG bound to the translating ribosome
Structural highlights
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Function[RL21_ECOLI] This protein binds to 23S rRNA in the presence of protein L20.[HAMAP-Rule:MF_01363] [RL4_ECOLI] One of the primary rRNA binding proteins, this protein initially binds near the 5'-end of the 23S rRNA. It is important during the early stages of 50S assembly. It makes multiple contacts with different domains of the 23S rRNA in the assembled 50S subunit and ribosome.[1] Protein L4 is a both a transcriptional repressor and a translational repressor protein; these two functions are independent of each other. It regulates transcription of the S10 operon (to which L4 belongs) by causing premature termination of transcription within the S10 leader; termination absolutely requires the NusA protein. L4 controls the translation of the S10 operon by binding to its mRNA. The regions of L4 that control regulation (residues 131-210) are different from those required for ribosome assembly (residues 89-103).[2] Forms part of the polypeptide exit tunnel.[3] Can regulate expression from Citrobacter freundii, Haemophilus influenzae, Morganella morganii, Salmonella typhimurium, Serratia marcescens, Vibrio cholerae and Yersinia enterocolitica (but not Pseudomonas aeruginosa) S10 leaders in vitro.[4] [RL17_ECOLI] Requires L15 for assembly into the 50S subunit.[HAMAP-Rule:MF_01368] [RL18_ECOLI] This is one of the proteins that mediates the attachment of the 5S rRNA subcomplex onto the large ribosomal subunit where it forms part of the central protuberance. Binds stably to 5S rRNA; increases binding abilities of L5 in a cooperative fashion; both proteins together confer 23S rRNA binding. The 5S rRNA and some of its associated proteins might help stabilize positioning of ribosome-bound tRNAs.[5] [RL16_ECOLI] This protein binds directly to 23S ribosomal RNA and is located at the A site of the peptidyltransferase center. It contacts the A and P site tRNAs. It has an essential role in subunit assembly, which is not well understood.[HAMAP-Rule:MF_01342] [RL25_ECOLI] This is one of the proteins that binds to the 5S RNA in the ribosome where it forms part of the central protuberance. Binds to the 5S rRNA independently of L5 and L18. Not required for binding of the 5S rRNA/L5/L18 subcomplex to 23S rRNA.[HAMAP-Rule:MF_01336] [RL29_ECOLI] Binds 23S rRNA. It is not essential for growth.[HAMAP-Rule:MF_00374] One of the proteins that surrounds the polypeptide exit tunnel on the outside of the subunit. Contacts trigger factor (PubMed:12226666).[HAMAP-Rule:MF_00374] [FTSY_ECOLI] Involved in targeting and insertion of nascent membrane proteins into the cytoplasmic membrane. Acts as a receptor for the complex formed by the signal recognition particle (SRP) and the ribosome-nascent chain (RNC). Interaction with SRP-RNC leads to the transfer of the RNC complex to the Sec translocase for insertion into the membrane, the hydrolysis of GTP by both Ffh and FtsY, and the dissociation of the SRP-FtsY complex into the individual components.[6] [7] [8] [9] [10] [11] [RL20_ECOLI] One of the primary rRNA binding proteins, it binds close to the 5'-end of the 23S rRNA. It is important during the early stages of 50S assembly.[HAMAP-Rule:MF_00382] [RL14_ECOLI] This protein binds directly to 23S ribosomal RNA. In the E.coli 70S ribosome (PubMed:12809609) it has been modeled to make two contacts with the 16S rRNA of the 30S subunit, forming part of bridges B5 and B8, connecting the 2 subunits. Although the protein undergoes significant rotation during the transition from an initiation to and EF-G bound state, the bridges remain stable. In the 3.5 A resolved structures (PubMed:16272117) L14 and L19 interact and together make contact with the 16S rRNA in bridges B5 and B8.[12] Can also interact with RsfA, in this case bridge B8 probably cannot form, and the 30S and 50S ribosomal subunits do not associate, which represses translation.[13] [RL24_ECOLI] One of two assembly initiator proteins, it binds directly to the 5'-end of the 23S rRNA, where it nucleates assembly of the 50S subunit. It is not thought to be involved in the functions of the mature 50S subunit in vitro.[14] One of the proteins that surrounds the polypeptide exit tunnel on the outside of the subunit.[15] [RL9_ECOLI] One of the primary rRNA binding proteins, it binds very close to the 3' end of the 23S rRNA.[HAMAP-Rule:MF_00503] [SECY_ECOLI] The central subunit of the protein translocation channel SecYEG. Consists of two halves formed by TMs 1-5 and 6-10. These two domains form a lateral gate at the front which open onto the bilayer between TMs 2 and 7, and are clamped together by SecE at the back. The channel is closed by both a pore ring composed of hydrophobic SecY resides and a short helix (helix 2A) on the extracellular side of the membrane which forms a plug. The plug probably moves laterally to allow the channel to open. The ring and the pore may move independently. SecY is required to insert newly synthesized SecY into the inner membrane. Overexpression of some hybrid proteins has been thought to jam the protein secretion apparatus resulting in cell death; while this may be true, overexpression also results in FtsH-mediated degradation of SecY.[HAMAP-Rule:MF_01465] [RL10_ECOLI] Protein L10 is also a translational repressor protein. It controls the translation of the rplJL-rpoBC operon by binding to its mRNA.[HAMAP-Rule:MF_00362] [RL22_ECOLI] This protein binds specifically to 23S rRNA; its binding is stimulated by other ribosomal proteins, e.g. L4, L17, and L20. It is important during the early stages of 50S assembly. It makes multiple contacts with different domains of the 23S rRNA in the assembled 50S subunit and ribosome.[HAMAP-Rule:MF_01331_B] The globular domain of the protein is one of the proteins that surrounds the polypeptide exit tunnel on the outside of the subunit, while an extended beta-hairpin is found that penetrates into the center of the 70S ribosome where it lines the wall of the exit tunnel. Removal of most of this hairpin (residues 85-95) does not prevent its incorporation into 70S ribosomes. Two of the hairpin residues (91 and 93) seem to be involved in translation elongation arrest of the SecM protein, as their replacement by larger amino acids alleviates the arrest.[HAMAP-Rule:MF_01331_B] [RL13_ECOLI] This protein is one of the early assembly proteins of the 50S ribosomal subunit, although it is not seen to bind rRNA by itself. It is important during the early stages of 50S assembly.[HAMAP-Rule:MF_01366] [RL23_ECOLI] One of the early assembly proteins, it binds 23S rRNA; is essential for growth. One of the proteins that surround the polypeptide exit tunnel on the outside of the subunit. Acts as the docking site for trigger factor (PubMed:12226666) for Ffh binding to the ribosome (SRP54, PubMed:12756233 and PubMed:12702815) and to nascent polypeptide chains (PubMed:12756233).[HAMAP-Rule:MF_01369] [RL3_ECOLI] One of two assembly inititator proteins, it binds directly near the 3'-end of the 23S rRNA, where it nucleates assembly of the 50S subunit.[HAMAP-Rule:MF_01325_B] [SECE_ECOLI] Essential subunit of the protein translocation channel SecYEG. Clamps together the 2 halves of SecY. May contact the channel plug during translocation. Overexpression of some hybrid proteins has been thought to jam the protein secretion apparatus resulting in cell death; while this may be true it also results in FtsH-mediated degradation of SecY.[16] [RL6_ECOLI] This protein binds directly to at least 2 domains of the 23S ribosomal RNA, thus is important in its secondary structure. It is located near the subunit interface in the base of the L7/L12 stalk, and near the tRNA binding site of the peptidyltransferase center.[HAMAP-Rule:MF_01365] Gentamicin-resistant mutations in this protein affect translation fidelity.[HAMAP-Rule:MF_01365] [RL11_ECOLI] This protein binds directly to 23S ribosomal RNA. Forms the L11 stalk, which is mobile in the ribosome, indicating its contribution to the activity of initiation, elongation and release factors.[HAMAP-Rule:MF_00736_B] [RL15_ECOLI] This protein binds the 5S rRNA. It is required for the late stages of subunit assembly, and is essential for 5S rRNA assembly onto the ribosome.[HAMAP-Rule:MF_01341_B] [SECG_ECOLI] Subunit of the protein translocation channel SecYEG. Overexpression of some hybrid proteins has been thought to jam the protein secretion apparatus resulting in cell death; while this may be true it also results in FtsH-mediated degradation of SecY. Treatment with antibiotics that block translation elongation such as chloramphenicol also leads to degradation of SecY and SecE but not SecG. [RL5_ECOLI] This is 1 of the proteins that binds and probably mediates the attachment of the 5S RNA into the large ribosomal subunit, where it forms part of the central protuberance. Its 5S rRNA binding is significantly enhanced in the presence of L18.[HAMAP-Rule:MF_01333_B] In the 70S ribosome in the initiation state (PubMed:12809609) was modeled to contact protein S13 of the 30S subunit (bridge B1b), connecting the 2 subunits; the protein-protein contacts between S13 and L5 in B1b change in the model with bound EF-G implicating this bridge in subunit movement (PubMed:12809609 and PubMed:18723842). In the two 3.5 A resolved ribosome structures (PubMed:16272117) the contacts between L5, S13 and S19 are different, confirming the dynamic nature of this interaction.[HAMAP-Rule:MF_01333_B] Contacts the P site tRNA; the 5S rRNA and some of its associated proteins might help stabilize positioning of ribosome-bound tRNAs.[HAMAP-Rule:MF_01333_B] [SRP54_ECOLI] Involved in targeting and insertion of nascent membrane proteins into the cytoplasmic membrane. Binds to the hydrophobic signal sequence of the ribosome-nascent chain (RNC) as it emerges from the ribosomes. The SRP-RNC complex is then targeted to the cytoplasmic membrane where it interacts with the SRP receptor FtsY. Interaction with FtsY leads to the transfer of the RNC complex to the Sec translocase for insertion into the membrane, the hydrolysis of GTP by both Ffh and FtsY, and the dissociation of the SRP-FtsY complex into the individual components.[17] [18] [19] [20] [21] [22] [23] [RL19_ECOLI] This protein is located at the 30S-50S ribosomal subunit interface. In the 70S ribosome (PubMed:12809609) it has been modeled to make two contacts with the 16S rRNA of the 30S subunit forming part of bridges B6 and B8. In the 3.5 A resolved structures (PubMed:16272117) L14 and L19 interact and together make contact with the 16S rRNA. The protein conformation is quite different between the 50S and 70S structures, which may be necessary for translocation.[HAMAP-Rule:MF_00402] [RL2_ECOLI] One of the primary rRNA binding proteins. Located near the base of the L1 stalk, it is probably also mobile. Required for association of the 30S and 50S subunits to form the 70S ribosome, for tRNA binding and peptide bond formation. It has been suggested to have peptidyltransferase activity; this is highly controversial.[HAMAP-Rule:MF_01320_B] In the E.coli 70S ribosome in the initiation state it has been modeled to make several contacts with the 16S rRNA (forming bridge B7b, PubMed:12809609); these contacts are broken in the model with bound EF-G.[HAMAP-Rule:MF_01320_B] Publication Abstract from PubMedDuring co-translational protein targeting, the signal recognition particle (SRP) binds to the translating ribosome displaying the signal sequence to deliver it to the SRP receptor (SR) on the membrane, where the signal peptide is transferred to the translocon. Using electron cryo-microscopy, we have determined the structure of a quaternary complex of the translating Escherichia coli ribosome, the SRP-SR in the 'activated' state and the translocon. Our structure, supported by biochemical experiments, reveals that the SRP RNA adopts a kinked and untwisted conformation to allow repositioning of the 'activated' SRP-SR complex on the ribosome. In addition, we observe the translocon positioned through interactions with the SR in the vicinity of the ribosome exit tunnel where the signal sequence is extending beyond its hydrophobic binding groove of the SRP M domain towards the translocon. Our study provides new insights into the mechanism of signal sequence transfer from the SRP to the translocon. Structure of the quaternary complex between SRP, SR, and translocon bound to the translating ribosome.,Jomaa A, Fu YH, Boehringer D, Leibundgut M, Shan SO, Ban N Nat Commun. 2017 May 19;8:15470. doi: 10.1038/ncomms15470. PMID:28524878[24] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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