A Specific Bacterial Aminoacylase Cleaves Odorant Precursors Secreted in the Human Axilla

Abstract

Human axillary odor is known to be formed upon the action of Corynebacteria sp. on odorless axilla secretions. The known axilla odor determinant 3-methyl-2-hexenoic acid was identified in hydrolyzed axilla secretions along with a chemically related compound, 3-hydroxy-3-methylhexanoic acid. The natural precursors of both these acids were purified from non-hydrolyzed axilla secretions. From liquid chromatography/ mass spectrometry analysis, it appeared that the acids are covalently linked to a glutamine residue in fresh axilla secretions, and the corresponding conjugates were synthesized for confirmation. Bacterial isolates obtained from the human axilla and belonging to the Corynebacteria were found to release the acids from these odorless precursors in vitro. A Zn 2؉ -dependent aminoacylase mediating this cleavage was purified from Corynebacterium striatum Ax20, and the corresponding gene agaA was cloned and heterologously expressed in Escherichia coli. The enzyme is highly specific for the glutamine residue but has a low specificity for the acyl part of the substrate. agaA is closely related to many genes coding for enzymes involved in the cleavage of N-terminal acyl and aryl substituents from amino acids. This is the first report of the structure elucidation of precursors for human body odorants and the isolation of the bacterial enzyme involved in their cleavage.The axilla region of humans contains a dense arrangement of apocrine, eccrine, and sebaceous glands, and it is an everyday experience, that volatile substances emanating from these areas make a key contribution to human body odor. Although this odor is perceived by today's society as mainly unpleasant, several studies indicate that it may contain chemical signals that affect the menstrual cycle (1) or that may be involved in a major histocompatibility complex allele-dependent mate selection (2). These studies point to an important role of body odors in the evolutionary history of man.Sweat as it is secreted by axillary glands is odorless. Since the pioneering work of Shelley et al. (3), it is known that (a) the typical strong axilla odor can only be released from apocrine secretions, and (b) that the action of skin bacteria is needed to generate the odoriferous compounds from non-smelling molecules present in these secretions. Indeed, the axilla is a skin region supporting a dense bacterial population, which is dominated by the two genera Staphylococcus and Corynebacteria (4, 5). Most individuals carry a flora that is dominated by either one of these two genera, and a strong correlation was found between a high population of Corynebacteria and a strong axillary odor formation (4, 6). As a practical consequence of these findings, halogenated antibacterials and aluminum preparations for reducing the bacterial population have become the main active ingredient of commercial deodorants for the last 40 years. The scientific conclusion from this early work was that axilla secretions contain non-odoriferous precursors that must be transformed by bacterial en...

Facts, fallacies, fears, and frustrations with human pheromones

“…Recently, researchers at Givaudan (Natsch et al, 2003) identified 3-methyl-3-hydroxylhexanoic acid (HMHA) as an additional important axillary odor constituent; how-ever, the olfactory threshold for this compound has not yet been reported. Qualitatively, this compound has a cuminlike, "sweaty" note reminiscent of E-3M2H, but more pungent (data not shown).…”

“…The structure of ASOB1 remains to be fully elucidated but it too appears to carry acidic molecules. The Givaudan group (Natsch et al, 2003) has suggested that a nonodorous precursor they isolated, an amide of 3-methyl-3-hydroxylhexanoic acid and glutamine (N␣-3-hydroxy-3-methyl-hexenoyl-glutamine; HMHA-Gln), is the actual precursor. However, due to their collection procedure, it is difficult to say that the 3M2H and/or HMHA is not initially intercathelated within ApoD.…”

Body odour of monozygotic human twins: a common pattern of odorant carboxylic acids released by a bacterial aminoacylase from axilla secretions contributing to an inherited body odour type

“…The synthesis of reference compounds has been described before (Natsch et al 2003(Natsch et al , 2006.…”

“…The aqueous phase was lyophilized for 16 hours and re-suspended in 0.7 ml H 2 O. A 0.4 ml sample of this concentrated aqueous extract was treated with a large excess of the recombinant enzyme N-AGA (4.5 mg per sample, produced and purified as described before; Natsch et al 2003) to ensure complete hydrolysis of the Gln conjugates. After 4 hours incubation at 368 C, 30 ml of 1 M HCl and 50 mg NaCl were added and the sample was extracted with 100 ml methyl-tert-butyl-ether (MTBE).…”

“…They reported that (E )-3-methyl-2-hexenoic acid is the key odour component but they also found several other carboxylic acids. In our previous work (Natsch et al 2006), we had identified a series of 26 different carboxylic acids in axilla secretions, which are secreted as N a -acyl-glutamine-conjugates and which are released from these conjugates by the enzyme N a -acyl-glutamineaminoacylase (N-AGA) isolated from commensal skin bacteria inhabiting the human axilla (Natsch et al 2003(Natsch et al , 2006. We had shown that most of these acids are odorants and that they occur in different ratios on different individuals, but whether these ratios are stable over time and whether they are genetically fixed had not been investigated.…”