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  Indian J Med Microbiol
 

Figure 2: The increase in protein tyrosine phosphorylation during capacitation has been shown to be regulated by a cAMP-dependent pathway involving protein kinase A (PKA), receptor tyrosine kinase pathway, and by the nonreceptor protein tyrosine kinase pathway.[35] cAMP has been shown to activate PKA, which in turn regulates protein tyrosine phosphorylation.[48] The binding of PKA regulatory subunit to the AKAP family of proteins promotes an increase in tyrosine phosphorylation of sperm proteins by indirect activation of Tyrosine kinases (TKs).[174] In human sperm, AKAPs proteins, namely AKAP3 and FSP95, are the most prominent tyrosine phosphorylated proteins during capacitation. Receptors TK is transmembrane proteins having an extracellular ligand binding domain and an intracellular tyrosine kinase domain. Upon extracellular ligand binding, a receptor TK are activated and then phosphorylates it (autophosphorylation) or other proteins. By contrast, nonreceptor protein TK lacks a transmembrane domain, most are soluble intracellular proteins located in the cytoplasm, nucleus, or anchored to the inner leaflet of the plasma membrane. Tyrosine and protein phosphorylation of the sperm flagellar proteins leads to capacitation of human sperm.[47],[175],[176]

Figure 2: The increase in protein tyrosine phosphorylation during capacitation has been shown to be regulated by a cAMP-dependent pathway involving protein kinase A (PKA), receptor tyrosine kinase pathway, and by the nonreceptor protein tyrosine kinase pathway.<sup>[35]</sup> cAMP has been shown to activate PKA, which in turn regulates protein tyrosine phosphorylation.<sup>[48]</sup> The binding of PKA regulatory subunit to the AKAP family of proteins promotes an increase in tyrosine phosphorylation of sperm proteins by indirect activation of Tyrosine kinases (TKs).<sup>[174]</sup> In human sperm, AKAPs proteins, namely AKAP3 and FSP95, are the most prominent tyrosine phosphorylated proteins during capacitation. Receptors TK is transmembrane proteins having an extracellular ligand binding domain and an intracellular tyrosine kinase domain. Upon extracellular ligand binding, a receptor TK are activated and then phosphorylates it (autophosphorylation) or other proteins. By contrast, nonreceptor protein TK lacks a transmembrane domain, most are soluble intracellular proteins located in the cytoplasm, nucleus, or anchored to the inner leaflet of the plasma membrane. Tyrosine and protein phosphorylation of the sperm flagellar proteins leads to capacitation of human sperm.<sup>[47],[175],[176]</sup>