Ligand binding reveals a role for heme in translationally-controlled tumor protein dimerization.
The translationally-controlled tumor protein (TCTP) is a highly conserved, ubiquitously expressed, abundant protein that is broadly distributed among eukaryotes. Its biological function spans numerous cellular processes ranging from regulation of the cell cycle and microtubule stabilization to cell growth, transformation, and death processes. In this work, we propose a new function for TCTP as a "buffer protein" controlling cellular homeostasis. We demonstrate that binding of hemin to TCTP is mediated by a conserved His-containing motif (His76His77) followed by dimerization, an event that involves ligand-mediated conformational changes and that is necessary to trigger TCTP's cytokine-like activity. Mutation in both His residues to Ala prevents hemin from binding and abrogates oligomerization, suggesting that the ligand site localizes at the interface of the oligomer. Unlike heme, binding of Ca2+ ligand to TCTP does not alter its monomeric state; although, Ca2+ is able to destabilize an existing TCTP dimer created by hemin addition. In agreement with TCTP's proposed buffer function, ligand binding occurs at high concentration, allowing the "buffer" condition to be dissociated from TCTP's role as a component of signal transduction mechanisms.
Integrated Cellular Responses Laboratory, Virginia Bioinformatics Institute, Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America; Protein Signaling Domains Laboratory, Virginia Bioinformatics Institute, Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America.
Andrew T
AT
Lucas
Integrated Cellular Responses Laboratory, Virginia Bioinformatics Institute, Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America.
Xiangping
X
Fu
Integrated Cellular Responses Laboratory, Virginia Bioinformatics Institute, Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America.
JingJing
J
Liu
Protein Signaling Domains Laboratory, Virginia Bioinformatics Institute, Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America.
Mary K
MK
Brannon
Integrated Cellular Responses Laboratory, Virginia Bioinformatics Institute, Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America.
Jianhua
J
Yang
Protein Signaling Domains Laboratory, Virginia Bioinformatics Institute, Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America.
Daniel G S
DG
Capelluto
Integrated Cellular Responses Laboratory, Virginia Bioinformatics Institute, Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia, United States of America.
Carla V
CV
Finkielstein
D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D014408:Biomarkers, Tumor / Q000737:chemistry* / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D019295:Computational Biology; D003432:Cross-Linking Reagents; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D005453:Fluorescence; D006427:Hemin / Q000378:metabolism*; D006706:Homeostasis / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011485:Protein Binding; D014176:Protein Biosynthesis / Q000502:physiology; D011487:Protein Conformation; D016415:Sequence Alignment; D000090324:Tumor Protein, Translationally-Controlled 1; D014461:Ultracentrifugation
D014408:Biomarkers, Tumor; D003432:Cross-Linking Reagents; C000715647:TPT1 protein, human; D000090324:Tumor Protein, Translationally-Controlled 1; D006427:Hemin; D002118:Calcium