Biochemical and biophysical analysis of the intracellular lipid binding proteins of adipocytes.
Adipocytes express two lipid-binding proteins; the major one termed the adipocyte lipid-binding protein or aP2 (ALBP/aP2) and a minor one referred to as the keratinocyte lipid-binding protein (KLBP). In order to evaluate the potential physiological roles for these proteins, their biochemical and biophysical properties have been analyzed and compared. ALBP/aP2 and KLBP exhibit similar binding affinities for most long-chain fatty acids; however, ALBP/aP2 exhibits a two to three-fold increased affinity for myristic, palmitic, oleic and linoleic acids, the predominant fatty acids of adipocytes. As measured by guanidinium hydrochloride denaturation, the stability of ALBP/aP2 is nearly 3 kcal/mol greater than that of KLBP. While the pI of ALBP/aP2 was determined to be 9.0, that of KLBP is 6.5 suggesting differing net charges at physiological pH. Analysis of surface electrostatic properties of ALBP/aP2 and KLBP revealed similar charge polarity, although differences in the detailed charge distribution exist between the proteins. The distribution of hydrophobic patches was also different between the proteins,ALBP/aP2 has only scattered hydrophobic surfaces while KLBP has a large hydrophobic patch near the ligand portal into the binding cavity. In sum, these results point out that despite the striking similarity between ALBP/aP2 and KLBP in tertiary structure, significant differences in ligand binding and surface properties exist between the two proteins. Hence, while it is tempting to speculate that ALBP/aP2 and KLBP are metabolically interchangeable, careful analysis suggests that the two proteins are quite distinct and likely to play unique metabolic roles.
Simpson
M A
MA
Department of Biochemistry, University of Minnesota, St. Paul 55108, USA.
LiCata
V J
VJ
Ribarik Coe
N
N
Bernlohr
D A
DA
D000595:Amino Acid Sequence; D000818:Animals; D002352:Carrier Proteins / Q000737:chemistry*; D004305:Dose-Response Relationship, Drug; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D051379:Mice; D018345:Mice, Knockout; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018996:Myelin P2 Protein / Q000737:chemistry*; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins; D011485:Protein Binding; D017386:Sequence Homology, Amino Acid; D055672:Static Electricity
D002352:Carrier Proteins; C082667:Fabp5 protein, mouse; C086936:Fabp7 protein, mouse; D000071438:Fatty Acid-Binding Protein 7; D050556:Fatty Acid-Binding Proteins; D018996:Myelin P2 Protein; D009363:Neoplasm Proteins; D009419:Nerve Tissue Proteins