AlphaFold3-guided tracrRNA redesign yields small monomeric Cas12f RNPs

Although Cas12f (Cas14) is among the smallest Class 2 CRISPR (clustered regularly interspaced short palindromic repeats) effectors, it assembles into dimeric ribonucleoprotein (RNP) complexes with guide RNA, substantially increasing its functional size and limiting its suitability for gene editing and biosensing applications. To overcome this limitation, we systematically investigate the structural and functional roles of Cas12f dimerization using a combination of computational modeling and experimental validation. Structural analysis using Protein Data Bank data and AlphaFold-3 predictions revealed that the 5'-end sequence of tracrRNA is essential for dimer formation but dispensable for substrate cleavage. Based on this, we designed a truncated tracrRNA by removing 70 nucleotides from its 5'-end. This shortened tracrRNA successfully loaded into Cas12f to form a one guide RNA-one Cas12f monomer RNP. This functionally monomeric RNP demonstrated substantially enhanced trans-cleavage activity: 4.5-fold for ssDNA, 3.5-fold for dsDNA, and 2.5-fold for RNA, resulting in markedly improved detection sensitivity: 10-fold for ssDNA and dsDNA, and 4-fold for RNA. In addition, the functionally monomeric RNP exhibits cis-cleavage activity and gene editing efficiency comparable to that of the dimeric RNP, thereby restoring the advantage of Cas12f as a compact enzyme for in vivo gene editing. These results highlight that the functionally monomeric Cas12f RNP combines enhanced biosensing performance with retention of its uniquely compact size, benefiting gene editing applications.