Characterization of human variants in obesity-related SIM1 protein identifies a hot-spot for dimerization with the partner protein ARNT2

Biochem J. 2014 Aug 1;461(3):403-12. doi: 10.1042/BJ20131618.


The bHLH (basic helix-loop-helix) PAS (Per/Arnt/Sim) transcription factor SIM1 (single-minded 1) is important for development and function of regions of the hypothalamus that regulate energy homoeostasis and the feeding response. Low-activity SIM1 variants have been identified in individuals with severe early-onset obesity, but the underlying molecular causes of impaired function are unknown. In the present study we assess a number of human SIM1 variants with reduced activity and determine that impaired function is frequently due to defects in dimerization with the essential partner protein ARNT2 (aryl hydrocarbon nuclear translocator 2). Equivalent variants generated in the highly related protein SIM2 (single-minded 2) produce near-identical impaired function and dimerization defects, indicating that these effects are not unique to the structure of SIM1. On the basis of these data, we predict that other select SIM1 and SIM2 variants reported in human genomic databases will also be deficient in activity, and identify two new low-activity SIM1 variants (V290E and V326F) present in the population. The cumulative data is used in homology modelling to make novel observations about the dimerization interface between the PAS domains of SIM1 and ARNT2, and to define a mutational 'hot-spot' in SIM1 that is critical for protein function.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Amino Acid Substitution
  • Aryl Hydrocarbon Receptor Nuclear Translocator / chemistry
  • Aryl Hydrocarbon Receptor Nuclear Translocator / metabolism*
  • Basic Helix-Loop-Helix Transcription Factors / chemistry
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / metabolism*
  • Cell Nucleus / metabolism*
  • Cell Nucleus / ultrastructure
  • Databases, Genetic
  • HEK293 Cells
  • Humans
  • Immunohistochemistry
  • Immunoprecipitation
  • Models, Molecular*
  • Molecular Sequence Data
  • Mutation
  • Polymorphism, Single Nucleotide*
  • Protein Interaction Domains and Motifs
  • Protein Multimerization
  • Protein Transport
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / metabolism
  • Repressor Proteins / chemistry
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Sequence Alignment


  • ARNT2 protein, human
  • Basic Helix-Loop-Helix Transcription Factors
  • Recombinant Proteins
  • Repressor Proteins
  • SIM1 protein, human
  • SIM2 protein, human
  • Aryl Hydrocarbon Receptor Nuclear Translocator