Practice question

Extraction of integral membrane proteins for functional study demands detergent that disrupts lipid bilayer but avoids complete unfolding of polypeptide. Ionic strong detergents like SDS bind cooperatively to protein backbone at about one SDS per two amino acids, imparting negative charge, disrupting secondary structure and denaturing enzymes, suitable for electrophoresis but not activity assays. Non-ionic detergents Triton X-100, Nonidet P-40, dodecyl-beta-D-maltoside DDM and octyl glucoside are milder; they replace lipids around transmembrane helices forming protein-detergent micelles, maintaining helical packing and often preserving oligomerization and cofactor binding. Among options list, Triton X-100 is mildest retaining native structure of many receptors, transporters and photosynthetic complexes, though still can inactivate sensitive proteins. Sodium deoxycholate is bile salt anionic more denaturing, disrupting protein-protein contacts. Selection depends on protein stability: mild non-ionic for functional reconstitution, harsher ionic for size analysis. Thus Triton X-100 is preferred when aim is to maintain native conformation during solubilization for downstream assays and crystallization trials.