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.
Publication Source (Journal or Book title)
Molecular and Cellular Biochemistry
Simpson, M., LiCata, V., Coe, N., & Bernlohr, D. (1999). Biochemical and biophysical analysis of the intracellular lipid binding proteins of adipocytes. Molecular and Cellular Biochemistry, 192 (1-2), 33-40. https://doi.org/10.1007/978-1-4615-4929-1_4