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Casposase, a homolog of Cas1 integrase, is encoded by a superfamily of mobile genetic elements known as casposons. While family 2 casposase has been well documented in both function and structure, little is known about the other three casposase families. Here, we studied the family 1 casposase lacking the helix-turn-helix (HTH) domain from Candidatus Nitrosopumilus koreensis AR1 (Ca. N. koreensis). The determinants for integration by Ca. N. koreensis casposase were extensively investigated, and it was found that a 13-bp target site duplication (TSD) sequence, a minimal 3-bp leader and three different nucleotides of the TSD sequences are indispensable for target specific integration. Significantly, the casposase can site-specifically integrate a broad range of terminal inverted repeat (TIR)-derived oligonucleotides ranging from 7-nt to ∼4000-bp, and various oligonucleotides lacking the 5′-TTCTA-3′ motif at the 3′ end of TIR sequence can be integrated efficiently. Furthermore, similar to some Cas1 homologs, the casposase utilizes a 5′-ATAA-3′ motif in the TSD as a molecular ruler to dictate nucleophilic attack at 9-bp downstream of the end of the ruler during the spacer-side integration. By characterizing the family 1 Ca. N. koreensis casposase, we have extended our understanding on mechanistic similarities and evolutionary connections between casposons and the adaptation elements of CRISPR-Cas immunity.

Photodynamic therapy (PDT) combined with oxygenating strategies is widely employed in cancer treatment; however, oxygen-boosted PDT has failed to achieve an ideal effect due to the complexity, heterogeneity, and irreversible hypoxic environment generated by tumor tissues. With the emergence of Fe-dependent ferroptosis boasting reactive oxygen species (ROS) cytotoxicity as well, such a chemodynamic approach to cancer therapy has drawn extensive attention. In this study, hemoglobin (Hb) is connected with the photosensitizer chlorin e6 (Ce6) to construct a 2-in-1 nanoplatform (SRF@Hb-Ce6) with Sorafenib (SRF, ferroptosis promotor) loaded, combining oxygen-boosted PDT and potent ferroptosis. Benefiting from the intrinsic presence of Fe capable of binding oxygen, hemoglobin concurrently furnishes oxygen for oxygen-dependent PDT and Fe for Fe-dependent ferroptosis. Furthermore, amphiphilic MMP2-responsive peptide is incorporated into the skeleton of the nanoplatform to ensure drug-release specificity for safety improvement. Correlative measurements demonstrate the potentiation of PDT and ferroptosis with SRF@Hb-Ce6. More importantly, PDT strengthens ferroptosis by recruiting immune cells to secrete IFN-γ, which can sensitize the tumor to ferroptosis in our findings. The therapeutic effect of synergistic treatment with SRF@Hb-Ce6 in vitro and in vivo was proven significant, revealing the promising prospects of combined PDT and ferroptosis therapy with the 2-in-1 nanoplatform.

The lysine-proline-valine tripeptide (KPV) can transport into colorectal cancer (CRC) cells via oligopeptide transporter 1 (PepT1) selectively. Here, we successfully designed a fluorescent probe for PepT1 receptor-targeted CRC imaging. This probe consisted of the CuInS2/ZnS (CIS/ZnS) quantum dots (QDs) conjugated with KPV (QD-PAAO-KPV), exhibiting excellent near-infrared emission characteristics. The in vitro and in vivo results showed that the QD-PAAO-KPV was specifically and efficiently internalized in the PepT1-overexpressing colorectal Caco-2 tumor. In addition, it demonstrated that the probe possessed good biological activities. Thus, this study revealed that the probe QD-PAAO-KPV presented desirable targeting ability, showing promising prospects in CRC detection.