P1296 Exploring the role of BOC mutations in Crohn’s disease using whole exome sequencing and molecular dynamics simulation
Authors: Zeng C , Zhou J , Zhao X 
Published: January 2025

Abstract

Background
Crohn’s disease (CD) is a chronic inflammatory bowel disease, whose pathogenesis involves genetic component. In this study, BOC was identified as a potential risk gene for CD, whose gene product is a member of the cell adhesion molecule family. It is suggested that BOC binds to the N-terminus of Dhh protein (DhhN) through its Fn2-Fn3 domain, facilitating hh protein signal transduction. This signal has been shown to maintain endothelial cell barrier integrity, which is critical in the development of CD. Hence, we hypothesize that mutations in the BOC protein could alter its structure, impairing its ability to bind or release hh proteins, leading to abnormal hh signal transduction and affecting endothelial cell barrier function. Therefore, we employed molecular dynamics simulation to investigate the characteristics and affinity changes of the domain, and the domain with DhhN complex, both before and after mutation.

Methods
The target risk gene BOC was identified, and employed molecular dynamics simulation to investigate the characteristics and affinity changes of the BOC Fn2-Fn3 domain, and the domain with DhhN complex, both before and after mutation.

Results
1. From the list of gene mutations, 121 candidate risk genes were identified.
2. The target risk gene BOC was identified, which is highly expressed on the colorectal endothelial cell membrane surface, and its expression shows a difference between CD patients and normal colorectal tissues.
3. The Arg697 mutation leads to decreased flexibility and increased stability of the BOC Fn2-Fn3 domain.
4. The Arg697 mutation increases the affinity of the domain with the DhhN complex, adding to the number of key amino acids and hydrogen bonds maintaining the complex’s affinity.

Conclusion
1. Whole exome sequencing analysis revealed specific BOC gene mutations in CD patients, with differential expression between patients and healthy individuals suggesting an important role for BOC in CD.
2. Molecular dynamics simulations revealed that the Arg697 mutation increases the stability of BOC, and also showed increased stability and affinity of its binding with DhhN, which might prevent BOC from properly releasing hh proteins after binding, leading to abnormal hh signal transduction and thus impairing endothelial cell barrier function, which may promote the development and progression of CD.
3. The increased affinity of the complex following the Arg697 mutation is due to an increase in the number of key amino acid residues at the binding interface, resulting in more hydrogen bonds. Modifying these key amino acids to alter the affinity of the complex could normalize hh signal transduction, thereby restoring endothelial cell barrier function.

References
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