Yes, PROTEINS is a Scrabble word!

Letter values in Scrabble US: P 3, R 1, O 1, T 1, E 1, I 1, N 1, S 1.

Is it a valid word?

PROTEINS is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

any of a large group of nitrogenous organic compounds that are essential constituents of living cells; consist of polymers of amino acids; essential in the diet of animals for growth and for repair of tissues; can be obtained from meat and eggs and milk and legumes