Bovine Epidermal Fatty Acid-Binding Protein:  Determination of Ligand Specificity and Cellular Localization in Retina and Testis

Abstract

The fatty acid-binding protein (FABP) family consists of small, cytosolic proteins believed to be involved in the uptake, transport, and solubilization of their hydrophobic ligands. Members of this family have highly conserved sequences and tertiary structures. Using an antibody against testis lipid-binding protein, a member of the FABP family, a protein was identified from bovine retina and testis that coeluted with exogenously added docosahexaenoic acid during purification. Amino acid sequencing and subsequent isolation of its cDNA revealed it to be nearly identical to a bovine protein expressed in the differentiating lens and to be the likely bovine homologue of the human epidermal fatty acid-binding protein (E-FABP). From quantitative Western blot analysis, it was estimated that bovine E-FABP comprised 0.9%, 0.1%, and 2.4% of retina, testis, and lens cytosolic proteins, respectively. Binding studies using the fluorescent probe ADIFAB indicated that this protein bound fatty acids of differing levels of saturation with relatively high affinities. Kd values ranged from 27 to 97 nM. In addition, the protein was immunolocalized to the Müller cells in the retina as well as to Sertoli cells in the testis. The location of bovine E-FABP in cells known to be supportive to other cell types in their tissues and the ability of E-FABP to bind a variety of fatty acids with similar affinities indicate that it may be involved in the uptake and transport of fatty acids essential for the nourishment of the surrounding cell types.

Role of the Fatty Acid Binding Protein mal1 in Obesity and Insulin Resistance

“…These two proteins are 51% identical at the amino acid level and exhibit the same ␤-barrel structure distinctive of all FABPs, suggestive of similar in vivo functions (3,13). Biochemically, mal1 protein binds to the fatty acids that have been tested with similar selectivity and affinity as aP2 (3,13).…”

“…Biochemically, mal1 protein binds to the fatty acids that have been tested with similar selectivity and affinity as aP2 (3,13). Whereas some of the functions of these two proteins in adipocytes also appear to be similar, it is likely that they mediate specific functions as well.…”

“…Whereas mal1 is expressed in differentiated adipocytes (4) and macrophages (9), it is also found in other tissues and/or cell types, including skin, lens, lung, and brain (11)(12)(13)(14)(15). In wild-type adipocytes, aP2 represents the majority of FABP, whereas mal1 constitutes a minor FABP fraction (8).…”

Modulation of Cutaneous Fatty Acid-binding Protein mRNA Expression in Rat Adipose Tissues by Hereditary Obesity and Dietary Fats

“…However, its mRNA was later found to be expressed in various tissues including adipose tissue 5,8,9,[12][13][14][15][16][17][18][19][20][21][22][23] . Krieg et al 5) examined levels of C-FABP mRNA in mouse tissues, and found that the mRNA was most abundant in stratified epithelia of the epidermis and tongue.…”

Oligozoospermia with normal fertility in male mice lacking the androgen receptor in testis peritubular myoid cells

“…Furthermore, levels of seminal transferrin are proportional to sperm production in humans and might be an effective indicator of Sertoli cell function (32). Epidermal fatty acid-binding protein expression was found in Sertoli cells and proposed to be involved in uptake and transport of essential fatty acids for growth and function of the surrounding germ cells (33). A combined reduction in both transferrin and epidermal fatty acid-binding protein expressions might contribute to decreased Sertoli cell nourishing function in PM-AR Ϫ/y mice, resulting in decreased sperm count (Fig.…”