Final answer:
The kinase that phosphorylates eIF2, which inhibits its function in translation initiation, impedes protein synthesis by preventing the formation of the translation initiation complex. This phosphorylation is a critical regulatory point in protein synthesis and is particularly relevant in the context of certain neurodegenerative diseases, where increased phosphorylation levels of eIF2 are observed.
Step-by-step explanation:
The protein that adds terminal phosphates to inhibit the function of eIF2 during translation initiation is known as a kinase, specifically GCN2 in the context of amino acid starvation in yeast or eIF2 kinase in general. The action of this kinase results in the phosphorylation of eIF2, which alters its ability to bind to GTP and GDP, thus impeding the formation of the translation initiation complex. This phosphorylation event is significant because it is a regulatory mechanism; when eIF2 is phosphorylated, it cannot support the exchange of GDP for GTP, necessary for the initiation of translation. As a result, protein synthesis is inhibited, which is particularly relevant in neurodegenerative diseases like Alzheimer's, Parkinson's, and Huntington's, as higher phosphorylation levels of eIF2 have been observed in patients.
In eukaryotes, the translation initiation complex is essential to start the protein synthesis process, which involves the formation of a complex including the eIF2 protein, GTP, and the methionine initiator tRNA binding to the small 40S ribosomal subunit. When phosphorylated, eIF2 undergoes a conformational change that prevents it from binding to GTP, making it unable to initiate translation efficiently. This molecular mechanism is a crucial control step in the regulation of protein synthesis.