Membrane Protein Structure and Assembly

Ross DalbeyThe Ohio State UniversityDepartment of Chemistry

Structures and architectures

• Protein-lipid interactions

• Two architectures (at least)

• TM helices

• Connecting loops and tails

• The “positive inside” rule

Biological Membrane

Heijne Nature Reviews Molecular Cell Biology 7, 909–918 (December 2006) | doi:10.1038/nrm2063

Molecular Interactions in Membrane Proteins

Only two basic structures

TM helix lengths are typically 20-30 residues

(Bowie, JMB 272: 780)

Loops tend to be short(Tusnady & Simon, JMB 283:488)

The “positive inside” rule

N

N

N

C

C

C

Procoat Leader Peptidase MalF

Periplasm

Cytoplasm

InnerMembrane

Dalbey (1990) TIBS 15, 253-257

Topology can be manipulated

N N

NC

Periplasm

Cytoplasm

InnerMembrane

Assembly of Membrane Proteins

Cytochrome bo oxidaseLacY permease

III+IV I IIIII+IV I II

Cyto

F1Fo ATPase

Many membranes in a eukaryotic cell

Membrane translocation and insertion devices in bacteria and in the endoplasmic reticulum

The machinery that is involved in membrane protein insertion in E. coli

Xie and Dalbey (2008) Nature Reviews Micro 6, 235

Front to Front

The X-ray Structure of the SecY complex in Methanococcus jannaschii

Van den berg et al., 2004, Nature 427 36-44

Van den Berg et al (2004) Nature 427, 36

Different stages of translocation of a secretory protein

Recognition of a transmembrane helix by the Sec61 translocon

Hessa et al (2005) Nature 433, 377

Evolutionarily conserved YidC Family Members

Stuart and Neupert (2000) Nature (News and Views) 406, 575

Jim Samuelson

Samuelson et al., (2000) Nature, 406, 637-41

YidC is essential for cell viability

YidC depletion studies

Samuelson et al., 2000, Nature, 406, 637-641

Samuelson et al., 2000, Nature, 406, 637-641

Effect of YidC depletion on Sec-independent Membrane Insertion

 

 

Illustration of site-specific photocrosslinking

Chen et al. (2002) JBC, 277, 7670-7675

YidC and Ffh interact with Pf3 coat

N

N

+

- --

--

++

++

PMF

YidC

CC

Pf3 coat InsertionPf3 coat Insertion

YidC is a Membrane Protein Insertase for Sec-Independent

Proteins

Procoat InsertionProcoat Insertion

Dalbey and Kuhn (2004) J. Cell Biol. 166, 769

NADH-dehydro-genases Ubiquinol

Pool

CytochromeOxidasebo3

NADH NAD+ O2H2O

H+

H+

e- e- e-

H+H+H+

F0

F1

ATP synthase

Periplasm

Cytoplasm

Why is YidC essential for Bacteria?

Respiratory chain complexes in E. coli

Substrates for the YidC-only pathway

Pf3coat M13procoat F-ATPasesubunit c

N

N

N Periplasm

MscL

N

•YidC is required for membrane insertion of these substrates

•Pf3 coat can insert into proteoliposomes containing only YidC

Substrates for the YidC-Sec pathway

F1Fo-ATPasesubunit a

N

NPeriplasm

LacY

N

P1 C

C C

•YidC is required for membrane insertion of CyoA and subunit a

•YidC is required for the membrane protein folding of LacY

CyoA

YidC functions in the integration of TS into the membrane

Xie and Dalbey (2008) Nature Reviews Micro 6, 235

YidC functions in the folding of Lac permease

Nagamori et al. (2004) J. Cell Biol. 165, 53

Assembly of cytochrome bo oxidase

Dalbey et al (2011) Ann Rev Biochem, in press.

Assembly of F1Fo ATP synthase

Dalbey et al (2011) Ann Rev Biochem, in press

Conclusion

• α-helices and β-sheets are the basic membrane-spanning regions

• Positively charged residues control the membrane protein topology

• Sec translocase and YidC insertase are the devices used to insert proteins

• The bacterial YidC functions as a membrane chaperone and assembly factor