(A) KDEL – Golgi

(B) K-K/R-X-K/R – Lysosome

(C) SKL – Peroxisome

(D) NPVY – Endoplasmic reticulum

The correct answer to Q.38 is (C) SKL – Peroxisome, as SKL is the canonical C-terminal peroxisomal targeting signal PTS1 for matrix protein import.​

Correct Answer

Option (C) SKL – Peroxisome identifies the serine-lysine-leucine tripeptide as PTS1, recognized by PEX5 receptor for peroxisomal matrix import via ubiquitination and docking.​

Option Analysis

(A) KDEL – Golgi: Incorrect

KDEL (Lys-Asp-Glu-Leu) is an ER retention/retrieval signal; proteins escaping to Golgi are captured by KDEL receptors (KDELR) for COPI-mediated retrograde transport back to ER, not permanent Golgi targeting.

(B) K-K/R-X-K/R – Lysosome: Incorrect

KKXX or KXKXX (dilysine motifs) target ER membrane proteins for Golgi-to-ER retrieval via COPI coats; lysosomal targeting uses M6P (mannose-6-phosphate) on soluble enzymes or tyrosine motifs (YXXΦ), not dilysine.​

(C) SKL – Peroxisome: Correct

SKL and variants (e.g., SRL) at C-terminus serve as PTS1, binding PEX5/PEX7 receptors for translocation across peroxisomal membrane through TOM/TOP complex, essential for β-oxidation enzymes.​

(D) NPVY – Endoplasmic reticulum: Incorrect

NPVY resembles endocytic motifs (NPXY for AP-2/clathrin internalization from plasma membrane); ER uses KDEL (soluble) or KKXX (membrane), while NPVY relates to LDL receptor trafficking.​