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Structure of the Monoclinic-2 (Monocl-2) Crystal Form of Human Apolipoprotein C1
Structural highlights
FunctionAPOC1_HUMAN Appears to modulate the interaction of APOE with beta-migrating VLDL and inhibit binding of beta-VLDL to the LDL receptor-related protein. Binds free fatty acids and reduces their intracellular esterification.[1] Publication Abstract from PubMedHuman apolipoprotein C1 (APOC1) is a 57 amino acid long polypeptide that through its potent inhibition of cholesterol ester transferase protein helps regulate the transfer of lipids between lipid particles. We have now determined the structure of APOC1 in four crystal forms by X-ray diffraction. A molecule of APOC1 is a single, slightly bent, alpha helix having 13 to 14 turns and a length of about 80 A. APOC1 exists as a dimer, but the dimers are not the same in the four crystals. In two monoclinic crystals, two helices closely engage one another in an anti-parallel fashion. The interactions between monomers are almost entirely hydrophobic with sparse electrostatic complements. In the third monoclinic crystal, the two monomers spread at one end of the dimer, like a scissor opening, and by translation along the crystallographic a axis, form a continuous, contiguous, sheet through the crystal. In the orthorhombic crystals two molecules of APOC1 are related by a non-crystallographic twofold axis to create an arc of about 120 A length. This symmetrical dimer utilizes interactions not present in dimers of the monoclinic crystals. Versatility of APOC1 monomer association shown by these crystals is suggestive of physiological function. The Structure of Human Apolipoprotein C-1 in Four Different Crystal Forms.,McPherson A, Larson SB J Lipid Res. 2018 Dec 17. pii: jlr.M089441. doi: 10.1194/jlr.M089441. PMID:30559175[2] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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