Figure 15-8

The alternating NAG–NAM polysaccharide
component of bacterial cell walls.

分子量14.7 kDaで129個のアミノ酸からなる

X-Ray structure of HEW lysozyme. Primary structure of HEWlysozyme.

The polypeptide chain isshown with a bound(NAG)6 substrate (green)

Summary of the peptidoglycan biosynthesis pathway

Structural summary of high-molecularweight penicillin-binding proteins (PBPs).
(a) Representative members from thedifferent PBPs are shown in ribbon format.
From left to right, the items from the Protein
Data Bank (PDB) shown are S. aureusmonofunctional
glycosyltransferase peptidoglycan
polymerization (mGTPGP) (PDB code
3HZS), S. aureus PBP2 (PDB code 2OLU),
E. coli PBP1b (PDB code 3FWM), A.
aeolicus PBP1a (PDB code 2OQO),
Streptococcus pneumoniae PBP1a (PDB
code 2C6W), S. pneumoniae PBP1b (PDBcode 2BG1), S. aureus PBP2a (PDB code
1VQQ), and S. pneumoniae PBP2x (PDBcode 1QME), and they are represented by adomain-based schematic below theirstructures. (b) Model for a productive
complex of the GT peptidoglycanpolymerization (GTPGP) domain from S.
aureus PBP2 with the acceptor lipid II anddonor glycan chain. Shown next to thestructure (left) are the molecular structuresof lipid IV (middle; E-Z stereochemical
designation of cis/trans bonds of isoprenyl
groups not shown) and the donor strand
analog moenomycin (right). (c) Complex
structure of the Streptomyces R61 D,Dcarboxypeptidase/transpeptidase (TP)acylated by cephalosporin 1 (PDB code
1HVB) (left). The molecular structure of thenatural TP substrate D-Ala-D-Ala is shown(middle) along with the mimicking !-lactam
substrate analog cephalosporin 1, bound in
the active site (right). The blue highlighted
regions represent the functional groups on
the substrate molecule and theircorresponding groups on the antibiotic thatare used to mimic these groups.

Conceptual models of peptidoglycan organization include the (a) layered, (b) scaffold, and (c) disorganizedlayered arrangements. Panels a-c depict the disaccharides as green pills and the stretched peptide crosslinks as blue sticks. It is contested whether the glycans run parallel or antiparallel to each other, although seeSharif et al. (173) for an examination of the S. aureus peptidoglycan. (d ) Electron cryotomography of sacculi
isolated from C. crescentus strain CB15N, with a putative glycan 9-mer atomic model placed in density(inset). (e) Atomic force microscopy (AFM; left side of image is height, right side is phase components) imageof S. aureus division planes, showing the inherited rib and junction peptidoglycan “piecrust” featurescharacteristic of division in successive 90" planes.

( f ) AFM of the inner-facing surface of a B. subtilis peptidoglycan layer with increasing magnification and aschematic ( far right side), revealing the “twisted cable” architecture ( feature I, background B) in all four panels.
Panels g and h show the use of AFM and secondary cell wall polymer mutants to probe the nanoscalearchitecture of cell wall peptidoglycans in living gram-positive bacteria, using a topographic imaging
peptidoglycan localized as parallel lines [visible in both g and h panels, deflection image and adhesion force
map (from the square area shown in g), respectively, on the surface of these mutants. (i) AFM image of asingle Bacillus atrophaeus spore germinating under native conditions; the peptidoglycan cell wall structure isevident in the center of the image.

細胞質におけるペプチドグリカンプレカーサーの合成

電荷をもった物質の濃度差の持つエネルギー＋

Vo= 0 mVとすると

ここで平衡時を考えると------ネルンストの式

Vo= 0 mVとしたときの平衡時の電気化学ポテンシャル

平衡電位を求める

平衡膜電位の実際例

バクテリアの運動