Structural Validation of ORF104 in Streptococcus sanguinis: Identification of a Net-Positive Inducible Megapore for Targeted CANCER Therapy

This dataset characterizes ORF104, a 50-residue cationic amphipathic peptide from Streptococcus sanguinis. High-resolution modeling with AlphaFold 3 reveals a stimuli-responsive helical architecture consistent with membrane-disrupting activity. Biophysical Architecture Monomeric models show high-confidence α-helices (pLDDT > 90 in the core region). Multimeric assemblies (6 copies) display lower interface confidence (ipTM = 0.18), a pattern typical of inducible pore-forming peptides that remain dissociated in aqueous solution (ΔSASA ≈ 0) and only oligomerize upon lipid bilayer contact. Electrostatic Selectivity and Human Safety BLASTp analysis against the Homo sapiens proteome (taxid:9606) yielded no statistically significant hits (top E-value = 19, query cover = 16 %). With a net charge of +5, ORF104 preferentially targets negatively charged membranes typical of cancer cells (phosphatidylserine exposure), while displaying minimal predicted affinity for neutral healthy mammalian cells. Oligomeric Geometry and Lytic Potential The hexameric model forms a bundle with an estimated central lumen diameter of approximately 40 Å (preliminary PyMOL measurement). This architecture suggests a concentration-dependent pore-forming mechanism capable of direct membrane lysis, potentially bypassing classical chemoresistance pathways such as ABC-transporter efflux. Safety Switch – ORF527 ORF527, an anionic peptide (net charge ≈ -6) with high phenylalanine and serine content, is hypothesized to function as a co-evolved regulator. In a toxin-antitoxin-like model, it may neutralize excess ORF104 activity through electrostatic complexation, providing a potential control mechanism for systemic toxicity. Future Directions The next phase involves AWS-accelerated GROMACS molecular dynamics simulations to evaluate membrane insertion kinetics and 104-527 interaction in tumor-mimetic lipid environments. Subsequent in vitro validation (hemolysis assays, cancer vs. normal cell-line toxicity, and drug-conjugation studies) will be required to assess translational potential. Computational Methodology Hydrophobicity was assessed with Kyte-Doolittle (mean 1.105) and HeliQuest. Structural measurements and visualizations were performed in PyMOL 2.5.