BIMM 120 - Midterm 2 (Saier) - week 6

prokaryotic cytoskeletal proteins and their eukaryotic homologs

FtsZ (highly conserved cytosolic GTPase in most bacteria and many archaea) —> tubulin

TubZ (highly divergent tubulin relative, plays a role in plasmid segregation) —> tubulin

PhuZ (positions replicating bacteriophage DNA to cell’s center) —> tubulin

MreB —> actin

ParM (role in plasmid segregation) —> actin

Crescentin —> IFs

E. Coli plasmid segregation - SopA

a P-loop ATPase that segregates plasmids in E. Coli

different levels of oxygen utilization by microbes

aerobe - seek oxygen

anaerobe - flee oxygen

microaerophile - seek specific O2 concentration

gram+ vs gram- bacteria main difference

gram+ = only 1 inner membrane, thick peptidoglycan

gram- = has inner and outer membrane + a periplasm in between, has a thinner peptidoglycan layer, has lipopolysaccarides on outer membrane

4 secretion systems

Type I = ABC (ATP-binding cassette)

Type II = general secretory pathway (sec/tat)

Type III = Fla/Path

Type IV = Conj/vir

type I secretory system

ABC - strictly ATP dependent, transports proteins across both membranes in 1 step in gram- bacteria

inner membrane component = MFP/OMA, outer membrane component = OMP (outer membrane factors)

MFP links inner and outer membrane transport pathways together (in periplasm)

type II secretory system - tat

twin arginine targeting - transports fully folded proteins, brings from cytoplasm to periplasm

TatA+TatB —> channel for protein translocation

TatC - serve as specificity determinant for the complex, energy coupling for transport includes PMG

DON’T need ATP to export protiens

outer membrane component = MTB (main terminal branch) - transports from periplasm to outer membrane, connects sec/tat system, uses ATP-coupled transport

type II secretory system - sec

exports unfolded proteins onto periplasm, driven by ATP/GTP hydrolysis and also uses PMF

type III secretory system

found in gram-, allow protein secretion (usually virulence factors) across both membranes of cell envelope

shares homology with flagella proteins (injectisomes), often secretes proteins directly into host cell cytoplasm

driven by ATP

type IV secretory system

have multiple subunits that span 2 membranes and peptidoglycan wall of gram- bacteria or single membrane pilus of gram+ bacteria

export proteins and DNA-protein complexes of the cell into cytoplasm of recipient cell

ATP driven

outer membrane protein translocases

FUP (fimbrial usher protein) system and TPS (two-partner secretion) system

FUP

biogenesis of many fimbriae/pili in gram- bacteria, relies on sec system to bring stuff into halfway

sensing physical forces - the different -taxis

thermotaxis - based on temp

aerotaxis - based on oxygen

magnetotaxis - based on magnetic field

all involve MCPs

thermotaxis

MCPs involved:

Tsr - warm + serine receptor

Tar - warm & cold + asp/maltose receptor

Trg - warm sensor

Tap - cold sensor

thermotaxis - warm vs cold sensors

warm sensors - run as temp increase, tumble as temp decreases (net = heat seeking)

cold sensors - run as temp decrease, tumble as temp increases (net = cold seeking)

thermotaxis - why MCP has multiple methylation sites?

for sensing gradient concentrations: ie. Tar has 4

methylation determines warm/cold-seeking behavior: unmethylated = warm sensor, methylated = cold sensor

Tar also senses Asp (carbon + nitrogen) and maltose (carbon): low nutrient conditions = warm sensor, high nutrient conditions = cold sensor

aerotaxis

don’t detect oxygen with MCPs directly, use 2 independent MCPs:

Aer - detects FAD (O2 binds)

Tsr - detects pmf directly

magnetotaxis

via magnetosomes - made of magnetite in oxic conditions and greigite in anoxic conditions

generally same size in all organisms because at optimum size for single-domain crystals, surrounded by a lipid membrane

mech = bacteria align magnetosomes to long axis/cell poles and run/reverse, preferred direction = under epigenetic control

chromatophores

catalyze light-driven reactions —> PMF driven ATP synthesis, contain 4 pigmented complexes

outer membrane vesicle trafficking functions

deliver toxins to euk. cells, protein and dna transfer between bacterial cells, traffick cell-cell signals, deliver proteases + antibodies, remove harmful incorrectly folded proteins

outer membrane vesicle trafficking examples

PQS (a type of quorum sensing molecule) - cell-cell communication

OMVs (outer membrane vesicle) - transmit virulence factors to host cells

bacterial chaperonin

GroEL/GroES - heptameric like bacterial proteosomes, finishes protein folding for partially folded/misfolded proteins

powered by ATP hydrolysis

bacterial proteosomes

protein-degrading complexes, structure = heptameric, does pupylation where it marks proteins with pup for degradation

powered by ATP hydrolysis

adhesins and virulence - h. pylori

has only 1 adhesin - binds to fucose, humans that don’t add fucose to stomach mucus = immune to h. pylori because prevents h. pylori attachment/infection

adhesins and virulence - e. coli

has about 30 adhesins

adhesins and virulence - s. pyogeneo (strrep throat)

non-fimbrial adhesin - has 2 adhesins: F-protein binds fibronectin and M-protein binds keratinocytes —> both needed tgt to infect