Valine is one of the 20 most common natural amino acids on Earth, and is coded for in DNA. Nutritionally, valine is also an essential amino acid.
In Sickle Cell Anaemia, it subsitutes for the hydrophilic glutamic acid amino acid in haemoglobin, and because it is hydrophobic, the haemoglobin 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.