SRP72-Associated Bone Marrow Failure Syndrome
Dongyou Liu in Handbook of Tumor Syndromes, 2020
SRP72 constitutes part of a ribonucleoprotein complex (signal recognition particle [SRP] complex, or signal recognition particle), which interacts with the ribosome (the other ribonucleoprotein particle) and targets secretory proteins to the rough ER, prior to integration into transmembrane or secreted proteins. Specifically, SRP72 and other SRP proteins (SRP9, SRP14, SRP19, SRP54, SRP68) bind the 7S RNA of ∼300 nt to form the SPR complex (either as monomers [SRP19 and SRP54] or heterodimers [SRP9/SRP14 and SRP68/SRP72]), which interacts directly with the docking protein in the ER membrane and mediates the transfer of integral membrane proteins and secretory proteins across the hydrophobic lipid bi-layers to the ER. The functionally independent Alu domain (SRP9/SRP14 and 5′/3′ ends of 7S RNA) in the SRP complex reaches into the factor binding site within the ribosomal 40S/60S subunit interface and is responsible for translation retardation (elongation arrest). The S domain (SRP19/SRP54/SRP68/SRP72) binds to the signal sequence emerging from the polypeptide exit tunnel in the signal pre-handover state. The multi-domain SRP GTPase SRP54 recognizes the signal with its M domain and establishes the targeting complex consisting of its NG domain bound to the homologous NG domain of the SRP receptor (SRαβ heterodimer) at the ER membrane in a GTP-dependent manner, which facilitates the targeting of ribosome bound nascent chain to the rough ER. Disassociation of the SRP complex from the ER allows resumption of elongation resumes and commencement of translocation [9,10].
Current and future CFTR therapeutics
Anthony J. Hickey, Heidi M. Mansour in Inhalation Aerosols, 2019
In human bronchial epithelial cells (HBECs), it was shown that amplifiers increased levels of immature F508del-CFTR more than the mature form (67). F508del-CFTR mRNA levels present at the ER were higher upon amplifier treatment, but to maintain this increase of CFTR, mRNA active translation was required (71). The first transmembrane domain (TM1) of CFTR acts as an inefficient signal sequence, which reduces effective membrane targeting for translation (72). In silico modeling of charged residues-to-alanine mutations residing in TM1, combined with in vitro experiments, demonstrated a lack of PTI-CH effectivity in these mutants (71). In the current model, PTI-428 and PTI-CH function by enhancing successful signal-sequence targeting of CFTR to the signal recognition particle (SRP), which in turn targets the ribosome-nascent chain complex to the translocon in the ER membranes for synthesis of the immature CFTR protein (69,71,73).
Introduction to Molecular Biology
Martin G. Pomper, Juri G. Gelovani, Benjamin Tsui, Kathleen Gabrielson, Richard Wahl, S. Sam Gambhir, Jeff Bulte, Raymond Gibson, William C. Eckelman in Molecular Imaging in Oncology, 2008
In mammalian cells, there are different compartments called organelles, which include the rough endoplasmic reticulum (ER), the smooth endoplasmic reticulum, the Golgi apparatus, the lysosomes, and the peroxisomes. In these cells, most proteins destined for secretion are targeted to the ER by a signal sequence at the amino end of the peptide, called signal peptide. This sequence is recognized by a signal recognition particle (SRP), which binds to the signal peptide. The protein-SRP complex can therefore bind to the SRP receptor on the target ER membrane. Proteins destined for other compartment are initially directed into the ER and will then follow the secretory pathway with similar signal peptides. This process is posttranslational and the proteins are packaged into vesicles as they move between the lumen of different organelles. After its synthesis, a protein can undergo some other posttranslational modifications while in these compartments. Basically, a protein is a simple chain of a combination of 20 different amino acids, but the post-translational modifications of these amino acids can extend the range of functions of this protein. A large variety of posttranslational modifications exists for proteins, including addition of functional groups by the processes of biotinylation, glycosylation and/or phosphorylation. Other forms of posttranslational modifications include the addition of other peptides, changes in the chemical nature such as deamidation, or structural changes such as addition of disulfide bridges. All these modifications will allow the production of the vast complexity of different protein types, from enzymes that catalyze fundamental reactions to antibodies participating in the immune response.
Endothelial cell-derived extracellular vesicles alter vascular smooth muscle cell phenotype through high-mobility group box proteins
Published in Journal of Extracellular Vesicles, 2020
Michael J. Boyer, Yayoi Kimura, Tomoko Akiyama, Ariele Y. Baggett, Kyle J. Preston, Rosario Scalia, Satoru Eguchi, Victor Rizzo
To gain a broader view of the effects of EC-derived EV on VSMC phenotype, we performed unbiased mass spectroscopy analysis on VSMCs following incubation with the EVs derived from ECs. Using a cut-off for peptide fold-change at 1.5, we identified several peptides that were up-regulated in VSMC upon EC EV incubation (Figure 6, Online Figure X and Online Table VI). Gene ontology analysis and interactome analysis suggest that EC EVs induce VSMC proteins involved in metabolic regulations including those involved in mitochondrial respiration and response to stress. Of note, among these altered proteins were the pro-hypertrophy molecule, ribosomal protein S6, and pro-inflammatory molecules, HMGB1 and HMGB2 on the peptide level. On the protein level, 4 proteins (Srprb, Maoa, Rhot2 and Kdelr2) were up-regulated (Online Table VII). Signal recognition particle receptor β (Srprb) is necessary for sorting secretory and membrane proteins to the endoplasmic reticulum membranes, suggesting up-regulation of membrane protein synthesis and excretion [46].
Full-length recombinant antibodies from Escherichia coli: production, characterization, effector function (Fc) engineering, and clinical evaluation
Published in mAbs, 2022
Md Harunur Rashid
Lee et al. used a signal recognition particle (SRP)-dependent cotranslational secretion signal sequence (DsbA) instead of a sec-dependent post-translational signal sequence (e.g., STII, pelB) to prevent aggregation in the cytoplasm and to improve secretion across the inner membrane.73 They achieved a titer of ~65 mg/L of a FL-IgG1 by simultaneous coexpression of Ffh (a component of the SRP pathway) and DsbC foldase and isomerase. In a separate study, they used a sec-dependent pelB signal sequence in conjunction with TIR optimization and DsbC overexpression and achieved a titer of ~362 mg/L IgG in a 5.5 L bioreactor after 22 h.74 More recently, in 2016, employing a host engineering approach that included PECS, the same team isolated mutants of the 16S rRNA gene, rrsE, and demonstrated its positive effect on SRP-dependent protein expression by achieving a titer of 0.4 g/L for IgG in high cell density fermentation (Table 2).75
How does an RNA selfie work? EV-associated RNA in innate immunity as self or danger
Published in Journal of Extracellular Vesicles, 2020
Yu Xiao, Tom Driedonks, Kenneth W. Witwer, Qian Wang, Hang Yin
Extracellular vesicles (EVs) are now known to be important carriers of both MAMPs and DAMPs. These sub-micron-sized, lipid bilayer-delimited particles are released from all investigated cell types, functioning to dispose of toxic material, provide trophic support, and shuttle molecular signals. In addition to exogenous MAMPs and the examples of endogenous PAMPs given above, EVs are also well known to carry an abundance of RNA biotypes. While microRNAs (miRNAs) [6] are by far the most studied, all other types of cellular RNAs can also be found in EVs [7]. For example, Y-RNA, 7SL and tRNA have been abundantly detected in EVs from various biological sources. In cells, 7SL forms an integral part of the signal recognition particle (SRP), which mediates the translocation of nascent proteins across the ER membrane [8], and tRNA is essential in recruiting amino acids to ribosomes during protein translation. Y-RNA subtypes (hY1, hY3, hY4 and hY5 in human; mY1 and mY3 in mouse) are components of Ro ribonucleoprotein complexes, act as scaffolds for distinct subsets of effector proteins, and may regulate RNA degradation and DNA replication [9,10]. These different RNA types may be incorporated into EVs via exosome and ectosome/microvesicle biogenesis pathways, either by interactions with proteins or diffusion, and can activate innate immune sensors such as TLRs or the cytosolic RNA sensor RIG-I. However, how do these processes occur?