THE 3-FOR-ONE MODEL FOR GRAM-NEGATIVE WALL GROWTH - A PROBLEM AND A POSSIBLE SOLUTION

Authors
Citation
Al. Koch, THE 3-FOR-ONE MODEL FOR GRAM-NEGATIVE WALL GROWTH - A PROBLEM AND A POSSIBLE SOLUTION, FEMS microbiology letters, 162(1), 1998, pp. 127-134
Citations number
20
Categorie Soggetti
Microbiology
Journal title
ISSN journal
03781097
Volume
162
Issue
1
Year of publication
1998
Pages
127 - 134
Database
ISI
SICI code
0378-1097(1998)162:1<127:T3MFGW>2.0.ZU;2-0
Abstract
The murein wall in Gram-negative bacteria is so thin that the mechanis m of growth is necessarily complicated. From analytical data of murein components, Holtje suggested a model for the growth mechanism that wo uld lead to safe wall enlargement. The model depended on the formation of trimers of peptidoglycan disaccharides linked via their pentapepti des. In the 'three-for-one' model three oligopeptidoglycan chains are linked to each other in the usual linkages between the carboxyl group of D-alanine residues and the E-amino group of diaminopimelic acid res idues; these are designated 'tail-to-tail' linkages. This three-chaine d raft is then linked to the stress-bearing wall via the formation of trimers, defined as three peptide chains linked together by tail-to-ta il linkages. Then by autolyzing the oldest bonds in each trimer, the o ld chain is excised and the raft becomes part of the stress-bearing wa ll and the wall is enlarged. There is a problem with the three-for-one model in that it demands a precise fitting of the prefabricated raft of three crosslinked chains to a stress-bearing chain in the wall fabr ic to allow the series of trimer linkages to form. Because the wall, w hen bearing stress, must be pulled into a 'honeycomb' structure, the e nd-to-end distance would be shortened. The possibility is raised here that the glycan chains in the stress-bearing wall are stretched to a s ufficient degree by the cell's turgor pressure to compensate for its z ig-zag structure; this could allow the model to function. A calculatio n is presented that assumes that the area of the pores in the fabric, called tessera, is maximized by the cell's turgor pressure. In this ca se the glycan chain must stretch 10% (and the end-to-end distance of p eptide strands stretch 28%) so that the end-to-end distance of a glyca n chain in the stress-bearing wall and the unstretched nascent wall ca n be the same and permit indefinite stable growth. (C) 1998 Federation of European Microbiological Societies. Published by Elsevier Science B.V.