IsoformMapper: A Web Application for Protein-Level Comparison of Splice Variants through Structural Community Analysis

Alternative splicing (AS) plays a key role in numerous cellular processes by enabling the existence of different protein isoforms with potentially different functions and fine-tuning isoform abundance. However, despite its biological importance, tools to compare the domain composition of AS-derived protein isoforms have lagged as they require both structural data and an appropriate methodology for isoform comparison. Recent advances in AI-driven protein structure prediction, particularly AlphaFold2, have made accurate structural determination of splicing isoforms easily accessible, paving the way for new tools to compare their structures and asses the functional consequences of AS at the protein structure level. Here, we present IsoformMapper, a web resource that enables researchers to study alternative splicing at the protein structural level using protein network community analysis, which captures 3D physical interactions between protein regions often missed by traditional domain analysis, allowing comparisons of isoforms across any biological system. As a proof of concept, we used our tool to a case study, in which we studied how GENOMES UNCOUPLED1 (GUN1) dependent retrograde signaling regulates plant de-etiolation through alternative splicing in Arabidopsis. In response to light, we demonstrate that GUN1 regulates the expression of specific spliceosome components, consequently modifying alternative splicing of key genes encoding components essential for establishing of photosynthesis. Additionally, the gun1 mutant showed altered splice variant ratios for PNSL2, CHAOS, and SIG5 . Our tool revealed that these isoforms have significantly different protein community structures, illustrating the impact of AS on protein function and demonstrating the practical value of the tool. (247 words)