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#lipid anchor

3 public questions tagged with this topic.

Lipid Link Protein

Which lipid anchor type is involved in signal transduction and is found in Ras protein?

Ras small GTPases H-Ras, N-Ras, K-Ras are central hubs in growth factor signaling linking receptor tyrosine kinases to Raf-MEK-ERK MAPK cascade regulating proliferation, differentiation, survival and cytoskeletal remodeling. For signaling competence Ras must associate with inner leaflet of plasma membrane where it interacts with effectors. This localization depends on C-terminal CAAX prenylation. H-Ras, N-Ras, K-Ras4A undergo farnesylation of CAAX cysteine by farnesyltransferase forming thioether linked 15-carbon anchor, followed by RCE1 cleavage and ICMT methylation. Additional second signal provided by palmitoylation of upstream cysteines for H-Ras and N-Ras or polybasic stretch for K-Ras4B enhances stable membrane binding and partitioning to distinct microdomains. GPI anchoring attaches extracellularly and myristoylation occurs at N-terminal glycine, not relevant to Ras, which is prenylated C-terminally. Oncogenic mutations lock Ras GTP-bound active causing constitutive signaling, making membrane association via farnesylation crucial therapeutic target for inhibitor development in cancer biology. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.

Ref: Hancock, Nat Rev Mol Cell Biol 2003, Ras membrane targeting; Prior et al., Cancer Res 2012.

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Lipid Link Protein

The lipid anchor in GPI-anchored proteins is attached to which part of the protein?

Glycosylphosphatidylinositol anchoring is complex post-translational modification processed in endoplasmic reticulum for about 150 human proteins destined for extracellular leaflet. Nascent proteins contain C-terminal hydrophobic signal peptide that is recognized by transamidase complex, cleaved after a specific omega residue, and replaced en bloc with preformed GPI moiety consisting of phosphatidylinositol lipid, glucosamine, three mannoses, phosphoethanolamine and galactose modifications. Attachment occurs to new C-terminus via amide linkage between protein carboxyl group and ethanolamine phosphate, positioning glycolipid anchor at extreme carboxyl end. This explains why internal lysine, N-terminus or mid-region attachments are incorrect; GPI always replaces C-terminal signal. Resulting GPI-anchored proteins orient extracellularly in lipid rafts, participating in adhesion, complement regulation, enzymatic activity and signal transduction. Examples include Thy-1, CD59 protectin, DAF, alkaline phosphatase and prion protein, cleavable by GPI-specific phospholipases for regulated shedding. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.

Ref: Fujita & Kinoshita, J Lipid Res 2012, GPI anchor biosynthesis and attachment.

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Lipid Link Protein

Which amino acid is commonly involved in myristoylation?

N-myristoylation is co-translational irreversible modification attaching 14-carbon saturated fatty acid myristate from myristoyl-CoA to target protein. N-myristoyltransferase NMT recognizes N-terminal sequence Met-Gly-X-X-X-Ser/Thr after methionine aminopeptidase removes initiator methionine, exposing glycine at position 2 for amide bond formation. The glycine requirement is absolute; replacement with other residues abolishes myristoylation. Myristate anchor provides weak membrane affinity that often cooperates with additional palmitoylation or polybasic cluster to stably tether proteins to inner leaflet of plasma membrane, Golgi and endomembranes. Src family kinases, MARCKS, recoverin and many viral proteins utilize myristoylation for membrane localization required for signal transduction, vesicular trafficking and assembly. Serine, cysteine and tyrosine are not acceptor sites for myristoylation; serine can be phosphorylated, cysteine palmitoylated or prenylated, and tyrosine sulfated or phosphorylated, highlighting glycine specificity that defines this lipid modification pathway in eukaryotes and some bacteria. Such detailed mechanistic insight is frequently examined in competitive tests including NEET, CUET, CSIR-NET and GATE where transporter classification, energetics and disease linkage are integrated into problem-solving questions.

Ref: Resh, Biochim Biophys Acta 1999, N-myristoylation mechanisms; Farah et al., J Biol Chem 2020, NMT specificity.

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