5me1
From Proteopedia
Structure of the 30S Pre-Initiation Complex 2 (30S IC-2) Stalled by GE81112
Structural highlights
Function[RS11_ECOLI] Located on the platform of the 30S subunit, it bridges several disparate RNA helices of the 16S rRNA. Forms part of the Shine-Dalgarno cleft in the 70S ribosome (By similarity).[HAMAP-Rule:MF_01310] [RS7_ECOLI] One of the primary rRNA binding proteins, it binds directly to 16S rRNA where it nucleates assembly of the head domain of the 30S subunit. Is located at the subunit interface close to the decoding center, where it has been shown to contact mRNA. Has been shown to contact tRNA in both the P and E sites; it probably blocks exit of the E site tRNA.[1] Protein S7 is also a translational repressor protein; it regulates the expression of the str operon members to different degrees by binding to its mRNA.[2] [RS17_ECOLI] One of the primary rRNA binding proteins, it binds specifically to the 5'-end of 16S ribosomal RNA. Also plays a role in translational accuracy; neamine-resistant ribosomes show reduced neamine-induced misreading in vitro.[HAMAP-Rule:MF_01345] [IF1_THET8] One of the essential components for the initiation of protein synthesis. Binds in the vicinity of the A-site (ECO:0000269|PubMed:11228145). Stabilizes the binding of IF-2 and IF-3 on the 30S subunit to which N-formylmethionyl-tRNA(fMet) subsequently binds. Helps modulate mRNA selection, yielding the 30S pre-initiation complex (PIC). Upon addition of the 50S ribosomal subunit IF-1, IF-2 and IF-3 are released leaving the mature 70S translation initation complex.[HAMAP-Rule:MF_00075][3] [RS18_ECOLI] Binds as a heterodimer with protein S6 to the central domain of the 16S rRNA, where it helps stabilize the platform of the 30S subunit.[HAMAP-Rule:MF_00270] [IF2_ECOLI] One of the essential components for the initiation of protein synthesis. Protects formylmethionyl-tRNA from spontaneous hydrolysis and promotes its binding to the 30S ribosomal subunits. Also involved in the hydrolysis of GTP during the formation of the 70S ribosomal complex.[HAMAP-Rule:MF_00100_B] [RS13_ECOLI] Located at the top of the head of the 30S subunit, it contacts several helices of the 16S rRNA.[4] In the E.coli 70S ribosome in the initiation state (PubMed:12809609) was modeled to contact the 23S rRNA (bridge B1a) and protein L5 of the 50S subunit (bridge B1b), connecting the 2 subunits; bridge B1a is broken in the model with bound EF-G, while the protein-protein contacts between S13 and L5 in B1b change (PubMed:12809609). The 23S rRNA contact site in bridge B1a is modeled to differ in different ribosomal states (PubMed:16272117), contacting alternately S13 or S19. In the two 3.5 angstroms resolved ribosome structures (PubMed:12859903) the contacts between L5, S13 and S19 bridge B1b are different, confirming the dynamic nature of this interaction. Bridge B1a is not visible in the crystallized ribosomes due to 23S rRNA disorder.[5] Contacts the tRNAs in the A and P sites.[6] The C-terminal tail plays a role in the affinity of the 30S P site for different tRNAs.[7] [A0A192C6K3_ECOLX] IF-3 binds to the 30S ribosomal subunit and shifts the equilibrum between 70S ribosomes and their 50S and 30S subunits in favor of the free subunits, thus enhancing the availability of 30S subunits on which protein synthesis initiation begins.[HAMAP-Rule:MF_00080][RuleBase:RU000646][SAAS:SAAS00636503] [RS6_ECOLI] Binds together with S18 to 16S ribosomal RNA.[HAMAP-Rule:MF_00360] [RS3_ECOLI] Binds the lower part of the 30S subunit head. Binds mRNA in the 70S ribosome, positioning it for translation (By similarity).[8] Plays a role in mRNA unwinding by the ribosome, possibly by forming part of a processivity clamp.[9] [RS9_ECOLI] The C-terminal tail plays a role in the affinity of the 30S P site for different tRNAs. Mutations that decrease this affinity are suppressed in the 70S ribosome.[10] [RS12_ECOLI] With S4 and S5 plays an important role in translational accuracy.[HAMAP-Rule:MF_00403_B] Interacts with and stabilizes bases of the 16S rRNA that are involved in tRNA selection in the A site and with the mRNA backbone. Located at the interface of the 30S and 50S subunits, it traverses the body of the 30S subunit contacting proteins on the other side and probably holding the rRNA structure together. The combined cluster of proteins S8, S12 and S17 appears to hold together the shoulder and platform of the 30S subunit (By similarity).[HAMAP-Rule:MF_00403_B] Cryo-EM studies suggest that S12 contacts the EF-Tu bound tRNA in the A-site during codon-recognition. This contact is most likely broken as the aminoacyl-tRNA moves into the peptidyl transferase center in the 50S subunit.[HAMAP-Rule:MF_00403_B] [RS20_ECOLI] Binds directly to 16S ribosomal RNA.[HAMAP-Rule:MF_00500] [RS14_ECOLI] Binds 16S rRNA, required for the assembly of 30S particles and may also be responsible for determining the conformation of the 16S rRNA at the A site.[HAMAP-Rule:MF_00537] [RS15_ECOLI] One of the primary rRNA binding proteins, it binds directly to 16S rRNA where it helps nucleate assembly of the platform of the 30S subunit by binding and bridging several RNA helices of the 16S rRNA.[HAMAP-Rule:MF_01343] In the E.coli 70S ribosome it has been modeled (PubMed:12809609) to contact the 23S rRNA of the 50S subunit forming part of bridge B4. In the two 3.5 A resolved ribosome structures (PubMed:16272117) there are minor differences between side-chain conformations.[HAMAP-Rule:MF_01343] [RS8_ECOLI] One of the primary rRNA binding proteins, it binds directly to 16S rRNA central domain where it helps coordinate assembly of the platform of the 30S subunit (By similarity).[HAMAP-Rule:MF_01302_B] Protein S8 is a translational repressor protein, it controls the translation of the spc operon by binding to its mRNA.[HAMAP-Rule:MF_01302_B] [RS4_ECOLI] One of two assembly initiator proteins for the 30S subunit, it binds directly to 16S rRNA where it nucleates assembly of the body of the 30S subunit.[11] [12] [13] With S5 and S12 plays an important role in translational accuracy; many suppressors of streptomycin-dependent mutants of protein S12 are found in this protein, some but not all of which decrease translational accuracy (ram, ribosomal ambiguity mutations).[14] [15] [16] Plays a role in mRNA unwinding by the ribosome, possibly by forming part of a processivity clamp.[17] [18] [19] Protein S4 is also a translational repressor protein, it controls the translation of the alpha-operon (which codes for S13, S11, S4, RNA polymerase alpha subunit, and L17) by binding to its mRNA.[20] [21] [22] Also functions as a rho-dependent antiterminator of rRNA transcription, increasing the synthesis of rRNA under conditions of excess protein, allowing a more rapid return to homeostasis. Binds directly to RNA polymerase.[23] [24] [25] [IF3_GEOSE] IF-3 binds to the 30S ribosomal subunit and shifts the equilibrum between 70S ribosomes and their 50S and 30S subunits in favor of the free subunits, thus enhancing the availability of 30S subunits on which protein synthesis initiation begins. [RS19_ECOLI] In the E.coli 70S ribosome in the initiation state (PubMed:12809609) it has been modeled to contact the 23S rRNA of the 50S subunit forming part of bridge B1a; this bridge is broken in the model with bound EF-G. The 23S rRNA contact site in bridge B1a is modeled to differ in different ribosomal states (PubMed:12859903), contacting alternately S13 or S19. In the 3.5 angstroms resolved ribosome structures (PubMed:16272117) the contacts between L5, S13 and S19 bridge B1b are different, confirming the dynamic nature of this interaction. Bridge B1a is not visible in the crystallized ribosomes due to 23S rRNA disorder.[HAMAP-Rule:MF_00531] Protein S19 forms a complex with S13 that binds strongly to the 16S ribosomal RNA. Contacts the A site tRNA.[HAMAP-Rule:MF_00531] [RS10_ECOLI] Involved in the binding of tRNA to the ribosomes.[HAMAP-Rule:MF_00508] [RS5_ECOLI] With S4 and S12 plays an important role in translational accuracy. Many suppressors of streptomycin-dependent mutants of protein S12 are found in this protein, some but not all of which decrease translational accuracy (ram, ribosomal ambiguity mutations).[26] Located at the back of the 30S subunit body where it stabilizes the conformation of the head with respect to the body.[27] The physical location of this protein suggests it may also play a role in mRNA unwinding by the ribosome, possibly by forming part of a processivity clamp.[28] Publication Abstract from PubMedIn bacteria, the start site and the reading frame of the messenger RNA are selected by the small ribosomal subunit (30S) when the start codon, typically an AUG, is decoded in the P-site by the initiator tRNA in a process guided and controlled by three initiation factors. This process can be efficiently inhibited by GE81112, a natural tetrapeptide antibiotic that is highly specific toward bacteria. Here GE81112 was used to stabilize the 30S pre-initiation complex and obtain its structure by cryo-electron microscopy. The results obtained reveal the occurrence of changes in both the ribosome conformation and initiator tRNA position that may play a critical role in controlling translational fidelity. Furthermore, the structure highlights similarities with the early steps of initiation in eukaryotes suggesting that shared structural features guide initiation in all kingdoms of life. Structure of a 30S pre-initiation complex stalled by GE81112 reveals structural parallels in bacterial and eukaryotic protein synthesis initiation pathways.,Lopez-Alonso JP, Fabbretti A, Kaminishi T, Iturrioz I, Brandi L, Gil-Carton D, Gualerzi CO, Fucini P, Connell SR Nucleic Acids Res. 2016 Dec 15. pii: gkw1251. PMID:27986852[29] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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