c-di-GMP

Question 1

what is c-di-GMP

Answer 1

a signalling molecule synthesised by DGC proteins with GGDEF and degraded by PDE proteins with either EAL or HD-GYP domains

Question 2

what is the function of input signalling REC protein domains

Answer 2

they are often associated with GGDEF domains and they are phosphorylated to activate c-di-GMP synthesis

Question 3

why is c-di-GMP classed as a second messenger

Answer 3

the first messenger is histidine kinase phosphorylating the REC domain

Question 4

how does c-di-GMP self regulate

Answer 4

it binds to the I site upstream of the catalytic domain which turns off the synthesis of c-di-GMP when levels are too high

Question 5

why is ancient evolution of the c-di-GMP signalling mechanism implied

Answer 5

there is a similar molecule, c-di-AMP, in archaea

Question 6

what do c-di-GMP levels indicate in terms of motility

Answer 6

high c-di-GMP levels mean more sessile and low c-di-GMP levels mean more motile

Question 7

what happens with high c-di-GMP levels in salmonella

Answer 7

cells adhere to each other in biofilms, and curli fimbriae and extracellular polysaccharides are produced

Question 8

what happens with low c-di-GMP levels in salmonella

Answer 8

altered gene expression results in the expression of flagella

Question 9

what are the two types of pili and what do they indicate

Answer 9

twitch pili indicate motility and curli pili indicate it’s sessile

Question 10

what is the trigger enzymes concept

Answer 10

GGDEF/DGC clump together so when one is activated the conformational change activates the rest

Question 11

how do c-di-GMP and PilZ work together by negative post translational control

Answer 11

they interact with FliM and Mot proteins at the base of the flagella to stop rotation

Question 12

how do c-di-GMP and PilZ work together by positive transcriptional control

Answer 12

it increases the expression of YcgR and BscA expression which both inhibit motility

Question 13

what are the roles of c-di-GMP in Caulobacter replication

Answer 13

levels control whether the cell is in stalked or swarmer format, and it controls chromosome replication via CckA kinase/phosphatase

Question 14

what is the implications of Bdellovibrio having such a large number of PilZ receptors

Answer 14

they are expressed in different places and at different times which reflects their complex life cycle

Question 15

what DCG proteins are needed in the predatory growth phase of the Bdellovibrio life cycle

Answer 15

DgcA and DgcB to positively regulate prey invasion and motility

Question 16

what DCG proteins are needed in the axenic growth phase of the Bdellovibrio life cycle

Answer 16

DgcC is required to positively regulate prey-independent growth

Question 17

what is GVNEF in Bdellovibrio

Answer 17

it is a degenerate GGDEF domain and acts as a receiver domain on receptor protein CgdA

Question 18

describe the mechanism by which Bdellovibrio contacts prey and initiates invasion

Answer 18

type IV PilA fibres pull the bacteria into contact with the prey cell. at the pole of contact are CdgA and DgcB which synthesises c-di-GMP to initiate predation

Question 19

how does DgcB self activate

Answer 19

it has a long protein chain which is forced into contact with its fork head FHA domain when in contact with prey. this causes a conformational change and causes activation of the GGDEF domain, also present on the DcgB protein, to stimulate the production of c-di-GMP

Question 20

in Vibrio cholerae in what ways are motility and virulence affected (2)

Answer 20

at high cell density LuxO cannot repress HapR. this HapR repressed TcpPH which results in the expression of viruence genes. HapR also prevents the expression of DCG proteins, therefore reducing the number of GGDEF domains which would normally promote biofilm formation, thus promoting motility and colonisation

Question 21

in Pseudomonas aeruginosa describe the process which results in the production of c-di-GMP when present in the lungs

Answer 21

presence on the lung surface is detected by WspA, which transduces this signal to receptor-kinase WspE. this phosphorylates WspR which synthesises c-di-GMp via its GGDEF domain

Question 22

in Pseudomonas aeruginosa what happens when c-di-GMP binds to PilZ proteins

Answer 22

there is production of cup-protein fimbriae and type III secretion apparatus for lung colonisation and virulence

Question 23

in Pseudomonas aeruginosa what happens when c-di-GMP binds to non-PilZ protin FleQ

Answer 23

it activates flagellar synthesis. it also represses the pel promoter, inhibiting the synthesis of EPS or biofilm gene expression and therefore promoting motility

Question 24

where does c-di-GMP bind to FleQ and how is this possible

Answer 24

it binds at the AAA+ATPase walker box motif. this is possible due to the structural similarity of ATPase and c-di-GMP