University:
Amherst College
Course:
BIOL 303 | Molecular Neurobiology: CURE
Academic year:

2009
Views:

98

Pages:

21
Author:

pureryohnl

Biochem 03 Cell Communication November 4, 2009 •Function: Signal Transduction • Long term acting signals –Steroid Hormones –Non Steroid Hormones (peptides) • Short term acting signals –Nitric oxide, NO Endocrine System • Small molecules are released from these glands into the bloodstream where they travel to a distant site and change the pace or architecture of the target tissue. • Hypothalamus in the brain is the mission control center Endocrine System Anterior Pituitary Posterior Pituitary Most of these are PEPTIDE HORMONES Hormones enter cells through different methods depending on their chemical nature Peptide hormones Steroid hormones Steroid Hormones • are small molecules • all exhibit lots of chemical similarity • all are fundamentally non-polar, hydrophobic Steroid Synthesis • derived from cholesterol • grouped by the receptors to which they bind: – glucocorticoids – mineralocorticoids – androgens – estrogens – progestagens – Vitamin D a sixth closely related hormone system with homologous receptors Action of Steroids – bind to receptors – complex migrates to the nucleus- binds to DNA – binding to DNA affects transcription – the pattern of gene expression is changed – the time scale for this event is slow (minutes to days) Nuclear Receptor Subfamily Yellow shows the highly variable activation domain Blue shows the highly conserved DNA binding domain- ~66 amino acids Red shows the hormone binding domain estrogen receptor glucocorticoid receptor Steroid Hormones Estrogen Receptor Hormone binding domain Estrogen Estradiol binds in a deep cleft of a binding site in this mostly helical 240 residue domain of ER. Somehow this gets communicated to DNA binding domain ER Hormone binding domain Structure 1A52 ER Hormone binding domain Structure 1A52 Hydrogen Bonds Ring A: Oxygen ___________ ___________ ___________ Ring D Oxygen ___________ ER Hormone binding domain Structure 1A52 Hydrophobic Int. @3.7 Å Ring A: Ring B: Now change distance to 3.8 Å and see what other interactions you see Steroid Receptors DNA binding domain • Zn finger proteins are the 2nd largest class of proteins • Genes for > 700 different Zn fingers in the human genome (antibodies largest) • DNA binding domain of a classic Zinc finger Zif268 shown left • the red helix interacts with the DNA…..How? Steroid Receptors DNA binding domain • Structural motif is highly versatile (one type of structure seems to be used in 700 different ways.) • # of Zn fingers in one protein ranges from 1 to 37 • Extended DNA sequences can be specifically recognized • Recognition happens through complementarity between amino acid side groups on helix (blue below) and base pair sequence of DNA Common Motifs in Steroid Receptors What the DNA looks like... • The DNA binding domain of the receptor binds to the hormone response element on the DNA • Changes of only two base pairs within each palindromic unit on the DNA switches the recognition from GR to ER Estrogen Receptor * DNA binding domain •Estrogen Receptor’s DNA binding domain also a zinc cluster protein. •Shown here is the DNA binding domain similar to glucocorticoid receptor ER DNA binding domain Structure 1hcq Do other types of molecules bind to this nuclear receptor subfamily? • Non-Natural non-steroidal ligands • Environmental Estrogens – Phytoestrogens from plants but remember plants don’t have cholesterol so must be non-steroidal pathways to derivatives. – Xenoestrogens - DDT is the most potent estrogenic mimic known, must stronger than estrogen itself in inducing proliferative cell growth, bisphenol A, THC, • see handout of xenoestrogens • see estrogen mimics under external links, signal transduction folder. Steroid Synthesis SQUALENE CHOLESTEROL • Steroid biosynthesis starts with the fatty acid squalene, whose carbon backbone is shown here • Synthesis occurs in the gonads and in the adrenal glands Glucocorticoid Receptor dimeric protein (blue and yellow balls above right) Each stabilized by a pair of zinc clusters (small purple balls) Recognition helix fits snugly into major groove of DNA, which widens 2 A in the process.

Biochem 03 Cell Communication Hormones November 4, 2009

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