Putative nucleotide-based second messengers in archaea

Second messengers transfer signals from changing intra- and extracellular conditions to a cellular response. Over the last few decades, several nucleotide-based second messengers have been identified and characterized in especially bacteria and eukaryotes. Also in archaea, several nucleotide-based second messengers have been identified. This review will summarize our understanding of nucleotide-based second messengers in archaea. For some of the nucleotide-based second messengers, like cyclic di-AMP and cyclic oligoadenylates, their roles in archaea have become clear. Cyclic di-AMP plays a similar role in osmoregulation in euryarchaea as in bacteria, and cyclic oligoadenylates are important in the Type III CRISPR-Cas response to activate CRISPR ancillary proteins involved in antiviral defense. Other putative nucleotide-based second messengers, like 3',5'- and 2',3'-cyclic mononucleotides and adenine dinucleotides, have been identified in archaea, but their synthesis and degradation pathways, as well as their functions as secondary messengers, still remain to be demonstrated. In contrast, 3'-3'-cGAMP has not yet been identified in archaea, but the enzymes required to synthesize 3'-3'-cGAMP have been found in several euryarchaeotes. Finally, the widely distributed bacterial second messengers, cyclic diguanosine monophosphate and guanosine (penta-)/tetraphosphate, do not appear to be present in archaea.

 

Comments:

The understanding of second messengers in archaea is an area of active research and your summary provides a concise overview of the current state of knowledge in this field.

Nucleotide-based second messengers play crucial roles in signal transduction pathways, allowing cells to respond to changing environmental conditions. In archaea, similar to bacteria and eukaryotes, several nucleotide-based second messengers have been identified, shedding light on the complexity of cellular signaling in these organisms.

1. **Cyclic di-AMP:** This molecule has been found to be involved in osmoregulation in euryarchaea, similar to its role in bacteria. Osmoregulation is vital for cells to maintain their internal environment in response to changes in external osmotic pressure.

2. **Cyclic oligoadenylates:** These molecules are significant in the Type III CRISPR-Cas response, where they activate CRISPR ancillary proteins involved in antiviral defense. This highlights the importance of second messengers in the adaptive immune systems of archaea, similar to their role in bacteria.

3. **Other putative nucleotide-based second messengers:**

 Various nucleotide-based molecules such as 3',5'- and 2',3'-cyclic mononucleotides and adenine dinucleotides have been identified in archaea. However, their specific functions as second messengers, as well as the pathways regulating their synthesis and degradation, are yet to be fully elucidated.

4. **3'-3'-cGAMP:** While this molecule has not been identified in archaea, the presence of the enzymes required for its synthesis in certain euryarchaeotes suggests the possibility of its existence in these organisms. Further research is needed to confirm its presence and understand its role if it is indeed present.

5. **Absence of certain bacterial second messengers:** Notably, cyclic diguanosine monophosphate and guanosine (penta-)/tetraphosphate, which are widely distributed in bacteria, do not appear to be present in archaea. This suggests divergence in the signaling pathways between these two domains of life.

In summary, the study of nucleotide-based second messengers in archaea is a promising field that holds the potential for discovering novel signaling pathways and mechanisms in these organisms. Ongoing research efforts are likely to uncover more details about the synthesis, degradation, and functions of these molecules, contributing to a deeper understanding of archaeal cellular signaling.

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