Ribbon structure of L-FABP (RCSB Protein Data Bank ID code: 2LKK) demonstrating the classic β-barrel (yellow β-sheets A–J) and α-helices (red) common to both human and rat L-FABPs [60]. Shown within the β-barrel are two bound oleic acids [60]. Key amino acids differentiating human and rat L-FABPs are designated as follows: 1) tyrosine (Y) in β-sheet A is found in both human and rat L-FABPs; 2) tyrosines (Y) in β-sheets C and J are found only in rat L-FABP; 3) three positively charged amino acids (+) in β-sheets B, D, and F in rat L-FABP are replaced by neutral amino acids in human L-FABPs; 4) threonine (T), a polar non-charged amino acid, is found at position 94 (*) in β-sheet G of both wild-type human and rat L-FABP, but is replaced by the smaller non-polar alanine (A) in the human L-FABP T94A variant.