Which of the following is/are extra-cellular matrix protein(s)?
Options:
(A) Myosin
(B) Fibronectin
(C) Lamin
(D) Collagen
Official Answer Key:
B;D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2026 Q.29)**
**1. Governing Concept**:
- **Topic**: Cell Biology & Extracellular Matrix (ECM) Components
- The animal extracellular matrix consists of fibrous structural proteins (collagens, elastins), adhesive glycoproteins (fibronectin, laminin), and proteoglycans embedded in a hydrated polysaccharide gel.
- In contrast, cytoskeletal filament proteins (tubulins, actins, lamins) and motor proteins (dynein, kinesin, myosin) are strictly intracellular.
**2. Option Analysis**:
- **Option (A) [Tubulin] is INCORRECT**: Tubulin ($\alpha/\beta$) is a globular cytosolic protein that polymerizes into intracellular microtubules.
- **Option (B) [Fibronectin] is CORRECT**: Fibronectin is a high-molecular-weight multidomain adhesive glycoprotein secreted into the ECM that links cell surface integrins to extracellular collagens.
- **Option (C) [Dynein] is INCORRECT**: Dynein is a minus-end-directed intracellular cytoskeletal motor protein that transports cargoes along microtubules.
- **Option (D) [Laminin] is CORRECT**: Laminin is a major heterotrimeric ($\alpha\beta\gamma$) glycoprotein constituent of the basal lamina / basement membrane in the ECM.
**3. Final Answer**:
- **Correct Options**: **B, D**
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