The structure of the lantibiotic lacticin 481 produced by Lactococcus lactis:location of the thioether bridges

AbstractThe lantibiotic lacticin 481 is a bacteriocin produced by Lactococcus lactis ssp. lactis. This polypeptide contains 27 amino acids, including the unusual residues dehydrobutyrine and the thioether-bridging lanthionine and 3-methyllanthionine. Lacticin 481 belongs to a structurally distinct group of lantibiotics, which also include streptococcin A-FF22, salivaricin A and variacin. Here we report the first complete structure of this type of lantibiotic. The exact location of the thioether bridges in lacticin 481 was determined by a combination of peptide chemistry, mass spectrometry and NMR spectroscopy, showing connections between residues 9 and 14, 11 and 25, and 18 and 26

Structural Features of the Final Intermediate in the Biosynthesis of the Lantibiotic Nisin. Influence of the Leader Peptide

The antimicrobial membrane-interacting polypeptide nisin is a prominent member of the lantibiotic family, the members of which contain thioether-bridged residues called lanthionines. To gain insight into the complex biosynthesis and the structure/function relationship of lantibiotics, the final intermediate in the biosynthesis of nisin A was studied by nuclear magnetic resonance spectroscopy. In aqueous solution the leader peptide part of this precursor adopts predominantly a random coil structure, as does the synthetic leader peptide itself. The spatial structure of the fully modified nisin part of the precursor is similar to that of nisin in water. The leader peptide part does not interact with the nisin part of the precursor molecule. Thus, these two parts of the precursor do not influence each other’s conformation significantly. The conformation of the precursor was also studied while complexed to micelles of dodecylphosphocholine, mimicking the primary target of the antimicrobial activity of nisin, i.e. the cytoplasmic membrane. The location of the molecule relative to the micelles was investigated by using micelle-inserted spin-labeled 5-doxylstearic acid. It was observed that the N-terminal half of the nisin part of the precursor interacts in a different way with micelles than does the corresponding part of mature nisin, whereas no significant differences were found for the C-terminal half of the nisin part. In this model system the leader peptide is in contact with the micelles. It is concluded that the strongly reduced in vivo activity of the precursor molecule relative to that of nisin is not caused by a difference in the spatial structure of nisin and of the corresponding part of precursor nisin in water or by a shielding of the membrane interaction surface of the nisin part of the precursor by the leader peptide. Probably a different interaction of the N-terminal part of the nisin region with membranes contributes to the low activity by preventing productive insertion. The residues of the leader peptide part just next to the nisin part are likely to contribute most to the low activity of the precursor.

Lipid Transfer Proteins Enhance Cell Wall Extension in Tobacco

Plant cells are enclosed by a rigid cell wall that counteracts the internal osmotic pressure of the vacuole and limits the rate and direction of cell enlargement. When developmental or physiological cues induce cell extension, plant cells increase wall plasticity by a process called loosening. It was demonstrated previously that a class of proteins known as expansins are mediators of wall loosening. Here, we report a type of cell wall–loosening protein that does not share any homology with expansins but is a member of the lipid transfer proteins (LTPs). LTPs are known to bind a large range of lipid molecules to their hydrophobic cavity, and we show here that this cavity is essential for the cell wall–loosening activity of LTP. Furthermore, we show that LTP-enhanced wall extension can be described by a logarithmic time function. We hypothesize that LTP associates with hydrophobic wall compounds, causing nonhydrolytic disruption of the cell wall and subsequently facilitating wall extension

Solution structure of the plant disease resistance-triggering protein NIP1 from the fungus Rhynchosporium secalis shows a novel beta-sheet fold

Activation of the disease resistance response in a host plant frequently requires the interaction of a plant resistance gene product with a corresponding, pathogenderived signal encoded by an avirulence gene. The products of resistance genes from diverse plant species show remarkable structural similarity. However, due to the general paucity of information on pathogen avirulence genes the recognition process remains in most cases poorly understood. NIP1, a small protein secreted by the fungal barley pathogen Rhynchosporium secalis, is one of only a few fungal avirulence proteins identified and characterized to date. The defense-activating activity of NIP1 is mediated by barley resistance gene Rrs1. In addition, a role of the protein in fungal virulence is suggested by its nonspecific toxicity in leaf tissues of host and non-host cereals as well as its resistance gene-independent stimulatory effect on the plant plasma membrane H+-ATPase. Four naturally occurring NIP1 isoforms are characterized by single amino acid alterations that affect the different activities in a similar way. As a step toward unraveling the signal perception/transduction mechanism, the solution structure of NIP1 was determined. The protein structure is characterized by a novel fold. It consists of two parts containing β-sheets of two and three anti-parallel strands, respectively. Five intramolecular disulfide bonds, comprising a novel disulfide bond pattern, stabilize these parts and their position with respect to each other. A comparative analysis of the protein structure with the properties of the NIP1 isoforms suggests two loop regions to be crucial for the resistance-triggering activity of NIP1.Klaas A. E. van't Slot, Harrold A. van den Burg, Cathelijne P. A. M. Kloks, Cornelis W. Hilbers, Wolfgang Knogge, and Christina H. M. Papavoin