Bioinformatics and phylogenetic analysis of cellular defense systems

Abstract

Prokaryotes are under constant threat from foreign genetic elements such as viruses and plasmids. To defend themselves against these genetic invaders prokaryotes have evolved extensive defense mechanisms, including CRISPR-Cas systems and prokaryotic Argonautes. Both systems utilize guide nucleic acids to precisely target complementary foreign nucleic acids, showcasing the versatility of nucleic acid-guided genetic regulation. CRISPR (Clustered Regularly Interspaced Short Palindromic Repeat) loci are repeat sequences that contain fragments of previously encountered genetic parasites. These loci are frequently flanked by CRISPR-associated (cas) genes essential for providing immunity against these invaders. In addition to the cas genes, CRISPRs often feature leader sequences positioned upstream of CRISPR loci, playing a crucial role in transcription and adaptation. While the diversity of CRISPR loci and cas genes has been extensively investigated, the diversity of CRISPR leaders has not been evaluated with the same level of rigor. Comprehensive bioinformatic evaluations have depicted diverse CRISPR-Cas system types throughout bacterial and archaeal genomes, highlighting the dynamic evolution between phages and bacteria. Although the CRISPR-Cas system's versatility has been co-opted for gene editing and diagnostics, current identification methods are limited. This study focusses on the diversity of CRISPR leader sequences and how the conserved sequence motifs can be used in enhancing detection capabilities, presenting potential biotechnological innovations. Similar to CRISPRs, Argonaute proteins rely on guide nucleic acids to identify complementary target sequences. Prokaryotic Argonautes (pAgos) are phylogenetically diverse which have often been overlooked. This research uncovers the rich diversity of pAgos, particularly focusing on their association with various genes and their associated effector proteins. This intricate relationship suggests a potentially multifaceted role for some pAgos in prokaryotic defense mechanisms.