A researcher is studying the structure of different hormone receptors. Receptor proteins are isolated and purified from a homogenized tissue sample. Detailed structural analysis shows that one of the proteins contains a 30-amino acid motif coordinating a zinc molecule, as shown in the image below. A receptor for which of the following hormones was most likely isolated in this experiment?

Question

A researcher is studying the structure of different hormone receptors.  Receptor proteins are isolated and purified from a homogenized tissue sample.  Detailed structural analysis shows that one of the proteins contains a 30-amino acid motif coordinating a zinc molecule, as shown in the image below.  A receptor for which of the following hormones was most likely isolated in this experiment?

Quizplus · Accepted Answer

11ec160b_36bf_bfad_9249_8b9d2f4c4e19_MD0001_00 The zinc-finger structure represents the most commonly identified DNA-binding domain in humans. Zinc-finger motifs are composed of chains of amino acids bound together around a zinc atom via linkages with cysteine (and sometimes histidine) residues. This forms a stable, finger-shaped structure containing 2 antiparallel β- strands and an α-helix. Unique combinations of amino acids as well as the specific histidine and cysteine linkages determine DNA-binding specificity. Many transcription factors use multiple zinc-finger motifs to recognize specific genes and alter their activity. Although most hormones alter transcription regulation to some degree in target cells, only intracellular receptors located in the cytoplasm or nucleus can act directly as transcription factors. These intracellular receptors typically bind lipid-soluble hormones because the ligand has to diffuse across the cell membrane to reach the receptor. Once bound to their ligand, these receptors bind directly to target DNA sequences via zinc fingers to regulate gene expression. Examples include steroid (eg, estrogen, aldosterone, cortisol), thyroid hormone, and fat-soluble vitamin receptors. In contrast, non-lipid-soluble hormones interact with transmembrane receptors found on the cell membrane. These receptors use a signal transduction cascade involving second messengers with subsequent activation of non-receptor-associated transcription factors; they do not contain DNA-binding domains. Examples include the G-protein-coupled receptors that bind ACTH, ADH, epinephrine, and glucagon (Choices A, B, C, and D) as well as receptors with intrinsic and associated tyrosine kinase activity (eg, insulin and growth hormone receptors, respectively) (Choices E and F). Educational objective: Zinc-finger motifs are composed of chains of amino acids bound together around a zinc atom via linkages with cysteine and histidine residues. They recognize specific DNA sequences and are used by many transcription factors to bind DNA and alter activity of target genes. Intracellular receptors that bind steroids, thyroid hormone, and fat-soluble vitamins act directly as transcription factors and contain zinc-finger binding domains. __________ References: The prokaryotic zinc-finger: structure, function and comparison with the eukaryotic counterpart. (http://www.ncbi.nlm.nih.gov/pubmed/26365095)

A Researcher Is Studying the Structure of Different Hormone Receptors