3'4 Membrane proteins

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Plasma Membrane (PM) proteins

• Types integral peripheral
• Transmembrane domain
• Lipid anchors
• Glycocalyx
• Cell Cortex

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3.4 Membrane proteins

• Each cell membrane has a set of specific membrane
  proteins that allows the membrane to carry out
  its distinctive activities.
• Types are
• Integral
• Transmembrane domain (TMD), single pass
• Multiple TMDs, multi-pass
• Lipid anchored covalently attached hydrocarbon
  chains
• Peripheral associated with membranes through
  interactions with integral proteins

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3.4 Schematic of membrane proteins in a lipid
bilayer
Figure 3-32
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Peripheral proteins are removed by ? pH or
salt Integral proteins are solubilized only with
detergent
pH or salt
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• Two types of detergent
• Nonionic preserves native structure
  interactions
• Ionicdenatures proteins

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• Anatomy of a Transmembrane Domain (TMD) eg.
  Glycophorin
• Approx. 20 hydrophobic amino acids
• Forms alpha helix-gt extends about 4 nm

• Notes
• charges prevent slippage
• Side chains interact w/ acyl chains (hydrophobic
  Van der Waals)
• CO imino NH of helix are H-bonded

Figure 3-33
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Prediction of a transmembrane domain By sequence
analysis hydropathy plot
hydropathy
Amino acids (from N to C)
Program moves window Over sequence
calculates Hydrophobic index
...KRLLLLIFTVVFVYFFVIIFAIED...
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Bacteriorhodopsin example of multipass (7
TMDs) Light-gtconf ?-gtH pumping through pore (!)
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3.4 Anchoring of integral proteins to the plasma
membrane by hydrocarbon chains
Question what will phospholipase do?
Figure 3-36
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• Glycocalyx surrounds exoplasmic face of PM
• Cell Cortex actin underlies cytoplasmic face of
  PM

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• Glycocalyx Functions
• Protection
• Lubrication
• Cell/cell recognition combinatorial
  potentialis vast! Simple exampleis blood groups

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Cortical Actin Network Function Integrity of
Shape w/ Flexibility in Red Blood Cell it is
specializedspokes of spectrin connected to PM
at junctional complexes.
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How was this info determined?
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SDS-PAGE analysis of RBC proteins after
treatments centrifugation Identifies soluble,
peripheral, and integral components.
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Protease protection identifies proteins and
domains of proteins inside a membrane