Delivering their messages: Exploring the pathways of ancient messengers cAMP and cGMP

A new study led by researchers at Weill Cornell Medicine shows that two very similar molecules with fundamental but contradictory signaling roles in most forms of life exert their distinct influence through subtle differences in their associations with their signaling partners.

In the study published March 27 in the Structural nature and molecular biologyIn this study, the researchers used exquisitely sensitive measurement techniques to reveal at the single-molecule level how the signaling molecules cAMP and cGMP bind to a family of pacemaker-channel ion channels, one of the major types of proteins that regulate their activities.

Ion channels are common features of cell membranes, and they control basic cell functions by allowing calcium, sodium, potassium, and other charged elements called ions to flow in and out of cells. Many ion channels can bind both cAMP and cGMP while being effectively opened by only one of them. The exact way in which the two molecules exert their different effects on ion channel activity has been a mystery.

The study details how cAMP/cGMP relates to ion channels and advances understanding of a fundamental aspect of cell biology. These findings could eventually inspire new therapies for disorders involving dysfunction of ion channels.

said senior study author Dr. Simon Schuring, professor of physiology and biophysics in anesthesiology at Weill Cornell Medicine.

Cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) are known as cyclic nucleotides: “cyclic” because their chemical structures have ring or ring forms, and “nucleotides” because they are part of the same family of molecules as the building blocks of nucleotides A and G of DNA. They appear to have evolved as multipurpose switches capable of regulating the activity of a wide range of different protein targets.

Often only one of them, cAMP or cGMP, is the activator, while the other does little or nothing directly on the target but can force it into an inactive state by binding to the same site, so the competition between the two molecules switches Channels open and close.

cAMP/cGMP-regulated proteins include a large class of ion channels called cyclic nucleotide (CNG) ion channels. CNG channels play an important role throughout the nervous system, including in the sensory neurons that mediate smell and vision, and in pacemaker cells that control the rhythm of the heartbeat.

Dr. Schuring, who helped pioneer the use of a sensitive measurement technique called atomic force microscopy (AFM), and Dr. Krina Nijmegen, an ion channel expert and professor of physiology and biophysics in anesthesiology at Weill Cornell Medicine, have already made significant progress in understanding how cAMP is regulated. cGMP for CNG channels. in 2018 paperfor example, used high-speed AFM to show how the bacterial CNG channel, SthK changes conformation when bound to channel-opening cAMP or the proximal channel-active cGMP.

In the new study they collaborated again and are also joined by molecular modeling expert Dr. Helmut Grobmüller from the Max Planck Institute for Interdisciplinary Sciences in Germany. Their main technology this time was a force-sensing method associated with AFM called AFM single-molecule force spectroscopy, which is sensitive enough to measure the binding force of just one cAMP or cGMP molecule to its binding site on the ion channel. With that, and with the help of computational modeling, they determined how cAMP and cGMP differ in binding strength and depth to the same binding site on SthK, through interactions with different combinations of atoms within the binding site.

The study’s first author, Dr. Yangang Pan, a postdoctoral researcher in Scheuring’s lab.

The SthK duct is just one model of mammalian CNG ducts, and the researchers plan future studies with mammalian CNG ducts. But they believe their SthK findings really shed light on the underlying mechanism of how cAMP and cGMP act as regulators in their many roles throughout biology.

“cAMP/cGMP-binding sites have been found not only on ion channels but also on signaling enzymes, transcription factors and other proteins,” said Dr. Nimigean. “We suspect that in each case, nature has fine-tuned how these proteins recognize cAMP/cGMP, according to the functions of these proteins.”