Glycosylation and Hydroxylation of Amino Acid Residues: Which Residues Can Be Modified
Glycosylation of Amino Acid Residues
Glycosylation is a prevalent form of post-translational modification in proteins, characterized by the enzymatic attachment of carbohydrate moieties to specific amino acid residues. This modification profoundly influences protein stability, enzymatic activity, and subcellular localization.
1. Asparagine Glycosylation (N-Glycosylation)
N-glycosylation represents one of the most common types of glycosylation, predominantly occurring at asparagine (Asn) residues within the consensus sequence Asn-X-Ser/Thr (where X denotes any amino acid except proline). This conserved motif is critical for proper glycan addition during protein maturation in the endoplasmic reticulum.
2. Serine/Threonine Glycosylation (O-Glycosylation)
O-glycosylation typically takes place on serine (Ser) and threonine (Thr) residues. It plays an essential role in modulating protein function and mediating complex signal transduction cascades, particularly in cell surface proteins and secreted factors.
Hydroxylation of Amino Acid Residues
Hydroxylation constitutes another important post-translational modification, involving the enzyme-catalyzed addition of hydroxyl (-OH) groups to specific amino acid side chains.
1. Proline and Lysine Hydroxylation
This modification primarily targets proline (Pro) and lysine (Lys) residues. Proline hydroxylation is crucial for stabilizing the triple-helix structure of collagen, while lysine hydroxylation contributes to histone modifications and plays a regulatory role in chromatin remodeling and gene expression.
These biochemical modifications not only modulate the physicochemical characteristics of proteins but also underpin a wide array of biological processes, including signal transduction, immune responses, and cell adhesion. A comprehensive understanding of their site specificity and functional relevance is fundamental for elucidating protein function and the molecular basis of disease.
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