[12] Reductive alkylation of lysine residues to alter crystallization properties of proteins.

TLDR: Amino acid analysis is the best way of determining the degree of modification of the lysine residues after reductive alkylation, and has the advantage of quantitatively defining the number of non-, mono-, di-, and tri-methylated lysin residues.

Abstract: Publisher Summary This chapter discusses the reductive alkylation of lysine residues to alter the crystallization properties of proteins. Chemical modification has played an essential role in the development of protein function. The reductive alkylation of lysine residues involves the initial formation of a Schiff base between the ɛ-amino group of a lysine residue and a ketone or aldehyde that is then reduced to a secondary or tertiary amine. In principle, a wide variety of alkyl moieties can be added to an amino group by reductive alkylation. In practice, the majority of cases employing this chemical modification have focused on adding methyl groups using formaldehyde because of the greater reactivity of formaldehyde than other ketones or aldehydes and because this modification has the mildest effect on the biochemical properties of a protein. The protocols described in the chapter are designed for complete modification of all available lysine residues. Amino acid analysis is the best way of determining the degree of modification of the lysine residues after reductive alkylation. It has the advantage of quantitatively defining the number of non-, mono-, di-, and tri-methylated lysine residues. It reveals the presence of any side reactions with other reactive amino acid side chains in a protein.