Valine is one of the 20 natural amino acids, and is coded for in DNA. Nutritionally, valine is also an essential amino acid.
In sickle-cell disease, it subsitutes for the hydrophilic amino acid glutamic acid in hemoglobin: Because it is hydrophobic, the hemoglobin does not fold correctly.
Valine is uncharged overall, as its R group is neutral, and the charges from its amino and carboxylic acid groups balance out: a zwitterion.
Foods that are good sources of valine include cottage cheese, fish, poultry, beef, peanuts, sesame seeds, and lentils.