2010 Bio 317 Lecture 3

2010 Bio 317 Lecture 3 - 1 Prof. William Collins OfFce: 534...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: 1 Prof. William Collins OfFce: 534 Life Sciences Building OfFce Hours: Mondays, 4:00 5:00 PM or by appointment Recommended Reading: Matthews, Chapters 4 & 5 BIO 317: Lecture 3 Membrane-Spanning Regions Most membrane-spanning regions of proteins are folded as -helices. Maximizes hydrogen bonds between polypeptide backbone Shields polypeptide backbone (hydrophilic) from hydrophobic core of lipid bilayer Most of the side chains are nonpolar (hydrophobic) Membrane proteins may have multiple membrane-spanning regions. 2 Localizing Likely -Helical Segments in a Protein For short segments of amino acids (10-20) calculate free energy needed for transition to aqueous environment (hydropathy index) Positive values indicate hydrophic region likely -helix Bacteriorhodopsin has seven membrane-spanning -helices and seven peaks in hydropathy plot Sacroplasmic Reticulum Ca ++ Pump Example of P-type Transport ATPase 10 transmembrane helices (3 of which line a central channel that spans the lipid bilayer) When not phosphorylated, two helices are disrupted (#4 & #6) and protein accepts Ca ++ from cytosol (Ca ++ binding site exposed). When phosporylated, rearrangement of helices releases Ca ++ on other side of membrane (lumen). 2 Localizing Likely -Helical Segments in a Protein For short segments of amino acids (10-20) calculate free energy needed for transition to aqueous environment (hydropathy index) Positive values indicate hydrophic region likely -helix Bacteriorhodopsin has seven membrane-spanning -helices and seven peaks in hydropathy plot Sacroplasmic Reticulum Ca ++ Pump Example of P-type Transport ATPase 10 transmembrane helices (3 of which line a central channel that spans the lipid bilayer) When not phosphorylated, two helices are disrupted (#4 & #6) and protein accepts Ca ++ from cytosol (Ca ++ binding site exposed). When phosporylated, rearrangement of helices releases Ca ++ on other side of membrane (lumen). 3 Many Ion Channels Exhibit Selectivity Conducts K + 10,000 times better than Na + . Cannot be explained by pore size. K + and Na + similar in size (actually Na + is smaller!) Cannot be explained by high afFnity K + binding sites. Would greatly slow conductance Example: Bacterial K + Channel is highly selective for K + Selectivity is due to the selectivity Flter formed by four identical protein subunits (two shown) each with two transmembrane helices connected to a short pore helix and a loop that protrudes into the channel. Together, they...
View Full Document

Page1 / 15

2010 Bio 317 Lecture 3 - 1 Prof. William Collins OfFce: 534...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online