Deciphering the RNA-binding protein network during endosomal mRNA transport

Area of Science:

• Molecular Biology
• Cell Biology
• Structural Biology

Background:

• Microtubule-dependent endosomal transport is vital for polar growth and cargo distribution.
• The molecular mechanisms linking messenger RNAs (mRNAs) to endosomal surfaces are not fully understood.
• RNA-binding proteins play critical roles in regulating mRNA localization and function.

Purpose of the Study:

• To elucidate the structural basis of mRNA-endosome association mediated by RNA-binding proteins.
• To investigate the function and binding characteristics of the MademoiseLLE (MLLE) domain in Rrm4.
• To explore the evolutionary conservation and mechanistic principles of MLLE domain-mediated interactions.

Main Methods:

• Structural analysis of the Rrm4 protein from *Ustilago maydis*.
• Comparative analysis of Rrm4's MLLE domain with canonical MLLE domains (e.g., Pab1).
• Prediction and experimental verification of Rrm4 interactors using identified binding motifs.
• Investigation of human MLLE domains (PABPC1, UBR5) to assess conserved interaction principles.

Main Results:

• Identified a novel MLLE domain variant in Rrm4, characterized by a seven-helical bundle and a distinct binding interface.
• Disclosed unique structural and binding characteristics of Rrm4's MLLE domain compared to Pab1's canonical MLLE domain.
• Deciphered the MLLE binding code, enabling prediction and confirmation of new Rrm4 interactors.
• Demonstrated conserved mRNA-binding principles involving MLLE domains in human proteins PABPC1 and UBR5.

Conclusions:

• Structural variations within the widely distributed MLLE domain dictate mRNA-binding specificity during endosomal transport.
• The study provides detailed mechanistic insights into how MLLE domains facilitate mRNA attachment to endosomes.
• Findings reveal conserved mechanisms for mRNA-protein interactions crucial for cellular processes across eukaryotes.