Tài liệu Báo cáo khoa học: Solution NMR structure of five representative glycosylated polyene

Solution NMR structure of five representative glycosylated polyene

macrolide antibiotics with a sterol-dependent antifungal activity

Laurent Volpon and Jean-Marc Lancelin

Laboratoire de RMN Biomole´culaire associe´ au CNRS, Universite´ Claude Bernard – Lyon 1 and Ecole Supe´rieure de Chimie

Physique & Electronique de Lyon, Villeurbanne, France

Glycosylated polyene macrolide antibiotics, as nystatins and

amphotericins, are amphiphilic structures known to exert

antifungal activity by disrupting the fungal cell membrane,

leading to leakage of cellular materials, and cell death. This

membrane disruption is strongly influenced by the presence

and the exact nature of the membrane sterols. The solution

structures of five representative glycosylated members, three

tetraenes (pimaricin, nystatin A1and rimocidin) and two

heptaenes (candidin and vacidin A) have been calculated

using geometric restraints derived from 1

H-NMR data and

random searches of their conformational space. Despite a

different apparent structural order, the NMR solutions

structure indicate that the hydroxyl groups all clustered on

one side of the rod-shaped structures, and the glycosyl

moieties are structurally conserved both in their conforma￾tion and their apparent order. The molecular structures

afford an understanding of their selective interaction with the

membrane sterols and the design of new polyene macrolides

with improved activities.

Keywords: antifungal antibiotics; polyene macrolides; sterol￾dependant antibiotics; NMR solution structure; 1, 3-polyols.

The vast family of polyenes antibiotics [1,2] includes

amphiphilic compounds mostly produced by Streptomyces

species with potent antifungal properties. Polyene macro￾lides are of an authentic clinical value for efficient therapies

against animals, and human infectious diseases caused by

pathogenic fungi. In particular, nystatin A1, amphotericin

B, and pimaricin (natamycin) are the most common

polyene macrolides used for the treatment of fungal

infections. Due to its particular low toxicity, pimaricin

also has been used for a decade as a food preservative [3,4]

allowed in the European Union (additive E235) and

USA for preserving foods from mold contamination and

possible inherent risks of mycotoxin poisoning. The

polyene macrolides target the cytoplasmic membranes of

fungi where they interact selectively with ergosterol,

causing a major disorganization of the membrane structure

[5] leading to the leakage of cellular materials and in turn

the cellular death.

Depending on their molecular structures, polyene

macrolides have a more or less toxicity, in part due to a

residual interaction with cholesterol in mammalian cyto￾plasmic membranes. This gives to polyene macrolides

therapies undesired hemolytic and nephrolytic side-effects.

Other relevant effects assigned to some polyene macro￾lides, such as antiviral properties against several groups of

enveloped viruses [6,7] or stimulation of the immune

response at lower concentrations [8,9], have been also

reported. These activities make of polyene macrolides a

source of lead structures for the engineering of future

molecules with improved medicinal purposes. In parti￾cular, the gene clusters involved in the biosynthesis of

pimaricin in S. natalensis [10,11] and nystastin in S. nour￾sei [12] have been recently cloned and new models for

their biosynthetic pathways been proposed. These new

insights make bioengineering possible for new polyene

macrolides in addition to chemical synthesis.

Despite their discovery over 50 years ago, the under￾standing of the selective affinity of polyenes macrolides

for sterols in biomembranes has yet no experimental

molecular explanation at atomic resolution. The con￾formational analysis of different members of the polyene

family is one important step essential in understanding

their structure-to-activity relationships. Three-dimen￾sional structures of only three polyene macrolides of

disparate nature and activity, have been described to

date. Amphotericin B [13,14] and roxaticin [15] were

solved by crystallography, while filipin III was solved

using solution NMR [16].

Full stereochemical information (with the exception of

one chiral center at position 42 of the vacidin A side chain,

Fig. 1) are available for at least five polyene macrolides that

belong to a group of polyenes specifically glycosylated by

mycosamine, a hexose of the D-series. The glycosylation by

an amino sugar occurs near a carboxylic acidic function of

the macrolide, so that these polyene macrolides are zwiter￾ionic in addition to being amphiphilic. Nystatin A1was the

first polyene macrolide discovered [17]. Its covalent struc￾ture (without stereochemistry) was confirmed in 1970 [18]

and 1971 [19]. Pimaricin, or natamycin [20], was isolated in

1957 [21] and its covalent structure was established by

Golding et al. [22]. Rimocidin from S. rimosus was reported

in 1951 [23] and its covalent structure finally described in

1977 [24]. Vacidin A, one of the main components of the

aureofacin complex from S. aureofaciens, belongs to the

Correspondence to J.-M. Lancelin, Laboratoire de RMN

Biomole´culaire, Universite´ Claude-Bernard – Lyon 1, Domaine

Scientifique de La Doua, CPE – Lyon, 43, boulevard du 11 Novembre

1918, F-69622 Villeurbanne cedex, France.

Fax/Tel.: + 33 4 72 43 1 3 95,

E-mail: [email protected]

Abbreviation: ROE, rotating frame Overhauser effect.

(Received 11 March 2002, revised 17 July 2002, accepted 23 July 2002)

Eur. J. Biochem. 269, 4533–4541(2002)
FEBS 2002 doi:10.1046/j.1432-1033.2002.03147.x