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#COPI

3 public questions tagged with this topic.

Protein Sorting and Trafficking

Which of the following does NOT require clathrin-coated vesicles?

Coat identity determines vesicle origin and destination providing directional logic to secretory pathway. COPII composed of Sar1 initiating curvature, inner adaptor Sec23-Sec24 binding cargo export signals, outer cage Sec13-Sec31 polymerizing into cuboctahedron operates exclusively at ER exit sites producing vesicles moving toward ERGIC and cis-Golgi carrying newly synthesized secretory proteins bearing ER exit motifs DXE, LXXLE. COPI composed of ARF1-GTP and heptameric coatomer operates reciprocally at Golgi rims and ERGIC retrieving material backward including KKXX membrane proteins and KDEL

Ref: Alberts et al., MBC: COPII ER-to-Golgi transport does not require clathrin coats.

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Protein Sorting and Trafficking

Which coat protein mediates retrograde transport from the Golgi to ER?

Retrieval pathways restoring escaped ER proteins and itinerant SNAREs rely on COPI coat protein complex I heptamer. COPI subunits alpha, beta, beta prime, gamma, delta, epsilon, zeta assemble 600 kDa coatomer. At Golgi cisternae and ERGIC tubules ARF1-GTP generated by GBF1 GEF recruits en bloc coatomer via gamma-beta-delta trunk interaction. Membrane deformation creates 50-60 nm vesicles containing cargo exposing KKXX or KXKXX dilysine motif at C-terminus binding WD40 propeller of alpha and beta prime COP subunits and KDEL receptor-cargo complexes where receptor tail contains KKXX-like signals

Ref: Alberts et al., MBC: COPI coat mediates retrograde Golgi-to-ER transport and retrieval.

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Protein Sorting and Trafficking

The primary function of coat proteins like COPI and COPII is:

Formation of transport vesicles requires peripheral coat proteins that deform donor membrane into bud and select cargo through direct recognition of sorting motifs. COPII coat assembly initiates when Sar1 activated by Sec12 GEF at ER exit sites embeds N-terminal amphipathic helix into ER membrane, recruiting Sec23-Sec24 heterodimer where Sec24 contains multiple cargo-binding sites for di-acidic Asp-X-Glu, di-phenylalanine and motifs presented by cargo receptors like ERGIC-53 and p24 family. Outer layer Sec13-Sec31 forms cuboctahedral cage providing curvature and scaffold. COPI coat activated b

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 13: COPI and COPII Vesicle Coats.

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