Abstract
<title>Abstract</title> <p> OCT4 is a pioneer transcription factor indispensable for cellular reprogramming and pluripotency. While structural variants like OCT1 and OCT6 share the canonical octamer DNA-binding motif (5'-ATTTGCAT-3'), they lack reprogramming capacity. Landmark experimental studies established that a 17-amino-acid alpha-helical linker dictates this functional specificity, yet a detailed structural-evolutionary mapping of this critical interface remains incomplete. Here, we present a systematic <italic>in silico</italic> comparative analysis profiling the sequence divergence, cross-species conservation, and spatial microenvironment of the POU–linker interface across mammalian orthologs. Utilizing multiple sequence alignments and structural microenvironment mapping via PDB/UniProt databases, we demonstrate near-absolute structural constraint (94.1% sequence identity) across mammalian species, marked strictly by a single conservative Alanine-to-Serine substitution at position 11. Spatial coordinate mapping reveals that the key functional residue Gln81 (Q81) operates within a complex, chemically mixed network stabilized by a direct hydrogen bond to Tyr25 of the POU-specific domain, rather than interacting with DNA. By systematically auditing alternatives—including the 9aaTAD transactivation motif and SOX2-binding topographies—our models provide an evolutionary rationale for why localized perturbations like the Q81R mutation selectively dismantle pluripotency networks while leaving baseline DNA-binding machinery intact. This work provides a refined computational framework to guide future molecular dynamics simulations and targeted wet-lab mutagenesis strategies. </p>