Cholera toxin, secreted by Vibrio cholerae in the intestine of an infected person, is a heterodimeric protein (AB). 

TLS Online TPP Program

#Id: 9058

#Unit 4. Cell Communication and Cell Signaling

Epinephrine --> Gαs-GTP-->Adenylyl cyclase-->cAMP-->PKA

TLS Online TPP Program

#Id: 9059

#Unit 4. Cell Communication and Cell Signaling

PKA always phosphorylates a serine or threonine residue that is located within the common sequence motif: X-Arg-(Arg/Lys)-X-(Ser/Thr)-Φ

TLS Online TPP Program

#Id: 9060

#Unit 4. Cell Communication and Cell Signaling

Increased cAMP; PKA active, increased glycogen breakdown, and decreased glycogen synthesis

TLS Online TPP Program

#Id: 9061

#Unit 4. Cell Communication and Cell Signaling

The GPK in skeletal muscle is a huge protein with multiple subunits:

Kinase subunit contains the catalytic activity that activates GP 

Regulatory subunits is the ubiquitous protein calmodulin

TLS Online TPP Program

#Id: 9062

#Unit 4. Cell Communication and Cell Signaling

GPK enzyme activity is increased either by phosphorylation of these two regulatory subunits by PKA or by Ca+2 binding to the calmodulin subunit; maximal activity requires both.

TLS Online TPP Program

#Id: 9063

#Unit 4. Cell Communication and Cell Signaling

Phosphorylation of PKA at threonine-197 leads to conformational change in the activation loop, that promotes binding of both ATP and its substrate proteins.

PKA can autophosphorylate itself on T197