Fatty acid-binding site environments of serum vitamin D-binding protein and albumin are different

Abstract

Vitamin D-binding protein (DBP) and albumin (ALB) are abundant serum proteins and both possess high-affinity binding for saturated and unsaturated fatty acids. However, certain differences exist. We surmised that in cases where serum albumin level is low, DBP presumably can act as a transporter of fatty acids. To explore this possibility we synthesized several alkylating derivatives of 14 Cpalmitic acid to probe the fatty acid binding pockets of DBP and ALB. We observed that N-ethyl-5-phenylisooxazolium-3′-sulfonate-ester (WRK ester) of 14 C-palmitic acid specifically labeled DBP; but p-nitrophenyl-and N-hydroxysuccinimidyl-esters failed to do so. However, p-nitrophenyl ester of 14 C-palmitic acid specifically labeled bovine ALB, indicating that the micro-environment of the fatty acid-binding domains of DBP and ALB may be different; and DBP may not replace ALB as a transporter of fatty acids. KeywordsFatty acid-binding by vitamin D binding protein (DBP) and albumin (ALB); serum transport of fatty acids; affinity labeling analogs of palmitic acid; affinity labeling of fatty acid binding sites of DBP and ALB

Synthesis of the Fungal Lipo‐Chitooligosaccharide Myc‐IV (C16:0, S), Symbiotic Signal of Arbuscular Mycorrhiza

“…Final methanolysis of the O ‐acetate groups, followed by hydrogenolysis of the Z‐group, gave the free chito‐oligosaccharide (CO) 30 23a. After chromatography on silica gel, this compound was subjected to selective N ‐acylation using an excess of palmitoyl chloride 31 37 by heating (40 °C) in the presence of NaHCO 3 . The target compound, Myc (C16:0, S) 3S , was purified by chromatography on silica gel (ethyl acetate/methanol/water, 5:2:1 as eluent) and gel filtration through a Sephadex G‐25 column.…”

Behind the scenes of vitamin D binding protein: More than vitamin D binding

“…palmitic acid) [87]. These results point towards a different binding and transport of various fatty acids between DBP and albumin [85].…”

“…The fatty acidbinding pockets of DBP and albumin have a different chemical/electronic environment. The fatty acid-binding site of DBP can only accommodate a polar and zwitterionic head group of palmitic acid, whereas a hydrophobic and hydrophilic head group at the carboxy-terminus are tolerated [85]. The molar ratio of fatty acids bound to albumin (1.8) is also much higher in comparison with DBP (0.4).…”

“…The shared physiologically function of all members of the albuminoid superfamily is the fatty acid binding capacity [85]. In comparison with albumin, a relatively weaker binding with fatty acids (Kd ¼ 10 5 e10 6 M À1 ) has been demonstrated for DBP, which explains the fact that DBP plays only a contributory role in the transport of fatty acids.…”

New perspectives on the vitamin D binding protein

“…Saturated and unsaturated free fatty acids (FFA) can bind DBP and ALB, although cross‐linking studies with derivatives of palmitic acid indicated differences in the FFA binding domains of ALB and DBP . Addition of unsaturated fatty acids reduced DBP affinity for 25D and 1,25D slightly, whereas saturated fatty acids did not .…”