The Lin28 cold-shock domain remodels pre-let-7 microRNA

Area of Science:

• Molecular Biology
• Developmental Biology
• Structural Biology

Background:

• Lin28 is an RNA-binding protein that regulates microRNA processing, specifically the let-7 family.
• Lin28 inhibits let-7 biogenesis in embryonic stem cells, preventing differentiation.
• Both RNA-binding domains (RBDs) of Lin28, the cold-shock domain (CSD) and zinc-knuckle domain (ZKD), are crucial for binding let-7 precursors and blocking maturation.

Purpose of the Study:

• To systematically investigate the nucleic acid-binding preferences of Lin28's RBDs.
• To determine the crystal structure of the Lin28 CSD with and without nucleic acids.
• To elucidate the distinct roles of CSD and ZKD in pre-let-7 binding and processing.

Main Methods:

• Systematic examination of nucleic acid-binding preferences of Lin28 RBDs.
• X-ray crystallography of the Lin28 CSD in the presence and absence of nucleic acids.
• Mutagenesis studies to assess the functional impact of CSD and ZKD interactions.

Main Results:

• Both Lin28 CSD and ZKD bind to single-stranded nucleic acids.
• ZKD specifically recognizes a conserved GGAG motif, while CSD exhibits limited sequence specificity.
• The isolated Lin28 CSD binds pre-let-7 with reasonable affinity, remodeling its terminal loop and Dicer cleavage site.
• CSD induces a conformational change in pre-let-7, facilitating subsequent ZKD binding to the GGAG motif.

Conclusions:

• Lin28 CSD and ZKD possess distinct nucleic acid-binding properties and cooperative functions.
• CSD initiates pre-let-7 remodeling, enabling specific ZKD recognition and inhibition of let-7 maturation.
• This detailed understanding of Lin28-let-7 interaction provides insights into developmental regulation and differentiation processes.