Naturally occurring deletion of Lys 107 does not alter lipid binding affinity of apolipoprotein A-I

ESMOND GEH; GONZALEZ MARINA CECILIA; DÍAZ LUDOVICO IVO; JOHN MELCHIOR; W. SEAN DAVIDSON; SHIMPI BEDI J; GARDA, H. A.

Chicago

Encuentro; Scientific Session of the American Heart Association (AHA); 2020

American Heart Association (AHA)

Human apolipoprotein A-I (apoA-I) is the major protein component of high-density lipoproteins (HDLs) that plays a pivotal role in lipoprotein metabolism. The deletion mutant Lys107del (∆K107) it?s a natural variant of apoA-I (Wt) related to early atherosclerosis and hypertriglyceridemia in carriers. While this mutant has been extensively studied, little information exists on the structural and functional basis for this phenotype. To investigate if alterations in oligomeric states of ∆K107 are involved in his pathogenicity, we used isolated chemically crosslinked oligomers (XL-oligomer) to investigate its structure and functionality in comparison with the Wt. Fluorescence measurements in monomeric, dimeric, trimeric and tetrameric Wt apoA-I showed highly similar spectra indicating similar environments for Trp residues. ∆K107 exhibited a slight red shift, likely due to the Lys deletion near a Trp residue, but also showed similar spectra in all oligomeric states. Upon incorporation into lipoprotein complexes, the same red shift has been observed in all oligomeric states of ∆K107. Native PAGE sizing of XL-oligomers and XL-oligomer-lipoprotein complexes showed a comparable distribution for both variants. All XL-oligomers form large (440-660KDa) lipoprotein complexes with DMPC; but not all could form the typical small (140KDa) lipoprotein complexes observed for uncrosslinked proteins. ∆K107 has been proposed to alter LDL or VLDL lipolysis by binding to these lipoproteins and altering lipolysis. However, native LDL (nLDL) binding assays showed no-differences between Wt and ∆K107 in profile and the amount of protein binding to the LDL. Our work shows that the physiological effects of the mutation are likely not related to their capacity to form Wt-same size oligomers or the capacity to interact with lipids.