CAAXmerkinnän

CAAXmerkinnän refers to a specific type of post-translational modification that occurs in proteins. The "CAAX" motif is a C-terminal tetrapeptide sequence that typically consists of a cysteine residue, followed by an aliphatic amino acid (A), any amino acid (A), and finally, a hydrophobic or aromatic amino acid (X). This sequence acts as a signal for a group of enzymes known as prenyltransferases to attach a lipid group to the cysteine residue. This lipid modification, known as prenylation or isoprenylation, is crucial for the proper localization and function of many proteins. It often anchors proteins to cellular membranes, facilitating their interaction with other proteins and signaling pathways. Examples of proteins that undergo CAAX box prenylation include Ras GTPases, nuclear lamins, and certain guanine nucleotide-binding proteins. The precise identity of the attached lipid (geranylgeranyl or farnesyl) can depend on the specific CAAX motif and the enzymes involved. This modification is a vital regulatory step in cellular processes, influencing protein trafficking, signal transduction, and cell growth.