MB4 lecture 3

membrane bending

what are the mechanisms for membrane bending?

spontaneous curvature

lipid asymmetry

asymmetrical protein insertion

protein scaffold

protein shape

protein crowding

gases

COP-associated proteins

why can gases contribute to membrane bending?

they can affect lipid distribution by partitioning into the hydrophobic core, which alters lateral pressure profiles and disrupts lipid domain equilibrium

what is the structure of myristic acid?

14 carbons, saturated

what is the structure of palmitic acid?

16 carbons, saturated

what is the structure of stearic acid?

18 carbons, saturated

what is the structure of oleic acid?

18 carbons, 1 double bond

what is the structure of linoleic acid?

18 carbons, 2 double bonds

what is the structure of arachindonic acid?

20 carbons, 4 double bonds

how does cholera toxin promote membrane bending?

through the binding of its beta subunit pentamer to a cell-surface ganglioside, which clusters lipids

what does PLM stand for?

polarised localisation microscopy

what is polarised localisation microscopy?

combines single molecule localisation microscopy with polarised total internal refection fluorescence microscopy to detect membrane orientation

how does polarised localisation microscopy distinguish between membranes of varying orientations?

due to the differential excitation of membrane-confined fluorophores depending on the linear polarisation of the incident excitation light

what causes the differential excitation during polarised localisation microscopy to allow it to distinguish between membrane orientations

photoswitchable probes maintain their fluorescence dipole moment in the plane of the membrane, such that membranes parallel to the coverslip are preferentially excited by incident s-polarised light, and membranes vertical to the coverslip are preferentially excited by incident p-polarised light

how an osmotic tension cause a shift in fluorescence output?

Lipid decompression, tail tilting, phase separation

what is the nuclear envelope?

double membrane surrounding the nucleus

describe the curvature of a nuclear pore complex

convex curvature along the surface of the membrane connection between the outer and inner nuclear membrane

concave curvature in the plane of the pore

what is the nuclear lamina?

network of proteins underneath the inner membrane that supports the nucleus and maintains nuclear shape

how does the nuclear lamina support the nucleus and maintain nuclear shape?

SUN domain proteins in the inner nuclear membrane connect the lamin nucleoskeleton to Nesprins in the outer nuclear membrane, which in turn connect to the cytoskeleton actin and intermediate filament networks

what happens when SUN proteins are disrupted and why?

the spacing between the two membranes becomes less regular, as SUN domain proteins and Nesprins help maintain correct spacing between the inner and outer membranes

why is the nuclear membrane needed to be dynamic?

nearly all higher eukaryotes undergo ‘open’ mitosis, where the nuclear envelope disassembles and reassembles each cell cycle

what are reticulons?

proteins that help create curved membrane structures

what does reducing reticulons cause?

interfered with nuclear envelope assembly

describe the protocol for using Xenopus egg extracts to investigate which proteins are required for nuclear envelope assembly

1. use detergent on membrane proteins to form micelles

2. remove a particular protein using antibodies

3. when the detergent is diluted, membranes can reform into vesicles

depletion of p97 blocks nuclear membrane fusion - what does this suggest and why?

p97 is involved in SNARE-dependent membrane fusion events, so this suggests that membrane fusion is important during nuclear envelope formation

what are the ways in which the nuclear envelope obtains more membrane?

membrane coming from the ER

vesicles fusing with the NE

new lipid synthesis by cells