The protein is also stable against staphylococcal proteases, just like lysostaphin. P5091 concentration However, there are SB-715992 in vitro stability differences in serum and blood. This would obviously be relevant if lysostaphin or LytM were used systemically. As we are not sure to what extent the proteolytic stabilities in blood or serum reflect the situation in tissues with eczema, the influence of this factor on the overall treatment income is not clear though should not be neglected. Binding Both lysostaphin and LytM185-316 bind the pentaglycine crossbridges of S. aureus peptidoglycan. Both proteins recognize the crossbridges themselves, probably at least in part by interactions with the
active site cleft. Lysostaphin has an extra cell wall targeting (CWT) domain which provides affinity. There is no counterpart in LytM (or LytM185-316), and therefore we originally expected that the N-terminal domain of the full length protein might play a similar role, especially in the light of the homology to SsaA. However, our experiments argue against this possibility, because full length LytM does not bind peptidoglycan. Modular STAT inhibitor structure LytM185-316 binds purified peptidoglycan the most effectively. The opposite is true for lysostaphin, which seems to recognize other cell wall components as well. It has previously been reported
that deletion of the CWT domain in lysostaphin does not interfere with the endopeptidase activity of the enzyme, but abolishes its ability to distinguish between S. aureus and S. staphylolyticus. As the peptidoglycans of the two bacterial species
are identical , it suggests the recognition of non-cell wall components by CWT. Irrespective of which part of the lysostaphin protein provides the affinity to non-peptidoglycan cell walls, the ability of the Monoiodotyrosine protein to bind to crude cell walls is clearly helpful to lyse intact cells and seems to provide lysostaphin with an advantage as a protein drug. LytM is an autolysin, which is produced by the cell and delivered to the cell wall from “inside” while lysostaphin is a bacteriocin that approach target cells from the “outside”. In the treatment model, the approach of the peptidoglycan hydrolases to cell walls is necessarily from the outside, again favouring lysostaphin over any LytM fragment. Ionic milieu Perhaps the most crucial factor to explain the different treatment outcomes is the very different response of the two proteins to the ionic milieu. We do not know the precise ionic milieu of the contact eczema model of S. aureus infection, but suspect that it belongs to the high ionic strength regime, which would certainly apply for serum. If this is true, the ionic milieu in the mouse eczema could explain differences in treatment outcomes between lysostaphin preferring higher concentrations of salts for its activity and LytM being strongly inhibited in such environment.