performed all other experiments

performed all other experiments. of these mAbs to detect structural transition of apoA-I on HDL. Importantly, a helix-disrupting mutation of W50R into residues 44C65 restored the immunoreactivity of mAbs whose epitope being within residues 44C65 against reconstituted HDL particles, indicating that these mAbs specifically recognize the epitope Tobramycin sulfate region in a random coil state. These results encourage us to develop mAbs targeting epitopes in the N-terminal residues of apoA-I as useful probes for monitoring formation and remodeling of HDL particles. Introduction Plasma levels of high-density lipoprotein (HDL) cholesterol are well known to be associated with a reduced risk of cardiovascular disease1, 2. The anti-atherogenic properties of HDL arise, in part, from its participation in the reverse cholesterol transport pathway in which the principal protein, apolipoprotein A-I (apoA-I), plays a central role3, 4. It is becoming apparent that the anti-atherogenic effects of HDL are not only dependent on its concentration in plasma but also on its biological functionality5C7 such as cholesterol efflux capacity from cells8, 9 and apoA-I exchangeability in which apoA-I can dissociate from the HDL surface and exchange between HDL particles10, 11. HDL particles are quite heterogeneous in their size, shape, and lipid and protein compositions12, 13. The heterogeneity of HDL particles primarily comes from the highly dynamic structure of apoA-I14, allowing it to adapt multiple lipid-bound conformations on HDL particles of different sizes and lipid and/or protein compositions3, 15C17. Upon HDL formation, apoA-I molecule undergoes a large conformational reorganization in which the opening of the N-terminal helix bundle occurs, converting hydrophobic helix-helix interactions to helix-lipid interactions3, 15, 18, 19. The apoA-I molecules in an anti-parallel, double-belt conformation stabilize nascent discoidal HDL particles of different sizes with certain segments forming flexible loops that detach reversibly from the surface20C22. In mature spherical HDL particles, the apoA-I molecules in the double-belt conformation bend and form a stabilizing trefoil scaffold structure16, 23. In addition, such conformational plasticity Mouse monoclonal to XRCC5 and flexibility of apoA-I are also thought to be associated with its strong amyloidogenic property24, 25. To discriminate the different apoA-I conformations on HDL particles, native monoclonal antibodies (mAbs) generated by hybridoma techniques targeting epitopes distributed along the apoA-I sequence26C32 as well as recombinant antibody fragments isolated from phage-displayed libraries33 have been used. A mAb that specifically recognizes an epitope of apoA-I exposed only in pre1-HDL (or lipid-poor apoA-I) has been commercially available to measure pre1-HDL concentration in plasma34, 35. In addition, mAbs that specifically recognize oxidized36, 37 or nitrated38 apoA-I in both lipid-free and HDL-bound forms have been developed to assess the distribution and function of modified, dysfunctional apoA-I in plasma as well as in artery wall. We previously developed a novel method for assessing HDL production from cells based Tobramycin sulfate on the lipidation-induced hydrophobicity Tobramycin sulfate change in apoA-I during HDL formation39. In this assay, we took advantage of a significant increase in fluorescence intensity when a fluorescence-labeled helix in apoA-I transfers from an aqueous environment to the hydrophobic lipid surface11, 15. In the present study, we focused on the fact that apoA-I molecule undergoes a large conformational transition in which the random coil regions both in the N-terminal and C-terminal domains form -helical structure upon lipid binding19, 21, 40, 41. To detect the secondary structural transition, we generated a panel of novel mAbs against human apoA-I, and found that mAbs that target epitopes in the N-terminal regions of apoA-I can recognize structural transition of apoA-I upon formation of HDL particles. The present results suggest that these mAbs may provide useful tools for monitoring formation and remodeling of HDL particles. Results.