Table of Contents

w232 Sal k 1 Scientific Information Summary Epidemiology Environmental Characteristics Clinical Relevance Molecular Aspects Diagnostic Relevance Compiled By

Component

w232 Sal k 1

w232 Sal k 1 Scientific Information

Type:

Component

Name; WHO/IUIS:

Sal k 1

Biological function:

pectin methylesterase

Allergen code:

w232

Source Material:

native (purified from pollen extract), N-methyl glycosylated protein

Other Names :

Salsola kali pectin methylesterase

Summary

Sal k 1 is a major allergen of the Russian thistle (Salsola kali) weed pollen. Sal k 1 belongs to the pectin methylesterase family and is N-glycosylated. Relevant cross-reactivity to Sal k 1 is limited to pollen homologues from other Salsola species. Of note, Chenopodium album, which grows in the same arid regions as S. kali, lacks a Sal k 1 homologue. Therefore, Sal k 1 sensitization is a marker of genuine sensitization to pollen from S. kali.

Epidemiology

Worldwide distribution

Russian thistle (Salsola kali) is a weed growing in a semi-desertic environment, naturally found in the Northern hemisphere and Australia, and widely employed for ornamental purposes under similar climate conditions [1, 2]. Therefore, S. kali is a major cause of pollen sensitization in exposed populations [1].

Sal k 1 is a major S. kali pollen allergen, binding IgE from 67% - 85% of patients sensitized to S. kali [2, 3]. The prevalence of Sal k 1 sensitization reached 71% in atopic asthmatic patients from Iran, greater than 18% seen with the next most frequent pollen allergens, grass components Phl p 1 and Phl p 5 [4]. At the low end, outside the geographical area of distribution of S. kali, the prevalence of Sal k 1 IgE is low, reported at 0.5% in a population of pollen-sensitized patients with doctor-diagnosed allergy [5].

Monosensitization to Sal k 1 is frequent in areas of high prevalence [1].

Environmental Characteristics

Source and tissue

Sal k 1 is present in S. kali pollen [3].

Risk factors

The main risk factor for developing sensitization to Sal k 1 is exposure to S. kali pollen [1].

Clinical Relevance

Detailed information regarding S. kali pollen is available in the whole allergen section. S. kali pollinosis manifests as allergic rhinitis and asthma

Disease severity and prediction

Sal k 1 sensitization is associated with intermittent allergic rhinitis, rhinoconjunctivitis, and asthma with a seasonal pattern [1, 6]. In atopic asthmatic patients from Iran, who displayed a 71% prevalence of Sal k 1 sensitization, no association was found between levels of Sal k 1 IgE and the severity of asthma [4].

Cross-reactive molecules

Sal k 1 exhibits limited cross-reactivity outside the Salsola genus [1, 2]. Cross-reactivity borne by Sal k 1 and its homologues may be low even among Salsola species, as reported in a study addressing IgE responses to S. kali and S. imbricata in patients living in Kuwait [6]. Proteins similar to Sal k 1 were reported in pollen from other weeds, such as Kochia scoparia, Salicornia sp and Arabidopsis thaliana as well as in tree pollen (e.g. Ole e 11), some plant foods, mainly Solanum tuberosum (potato), Arachis hypogea, Prunus dulcis, and Solanum esculentum [7, 8].

Molecular Aspects

Biochemistry

Sal k 1 has a molecular weight of 43 kDa, is found in multiple isoforms, and bears N-linked glycans [1, 2, 9]. Sal k 1 is a pectin methylesterase, belonging to a large multigenic family of enzymes involved in plant cell wall metabolism via demethyl esterification of galacturonic acid residues in pectin, a step resulting in either loosening or stiffening of the cell wall depending on the enzymatic partners involved [10, 11].

Isoforms, epitopes, antibodies

As of December 1st, 2021, four isoallergens of Sal k 1 have been included in the World Health Organization (WHO) and International Union of Immunological Societies (IUIS) Allergen Nomenclature [12], among six isoallergens reported in the literature [2].

Cross-reactivity due to structural similarity

Sal k 1 shares sequence identity of 57% with olive pollen pectin methylesterase, and at lower levels of 20% or less with plant food homologues found in kiwifruit, avocado, or pear [7].

Diagnostic Relevance

Marker allergen for genuine sensitization to Salsola pollens

Sal k 1 is a marker of genuine sensitization to S. kali pollen [1]. Inhibition experiments showed that Sal k 1 IgE accounts for 92% or the reactivity to S. kali extract [3]. In patients with IgE to plant carbohydrates, Sal k 1 IgE may be found positive due to N-glycosylation [1].

Cross-Reactivity

Sal k 1 cross-reactivity is limited to few weed pollen allergens, mainly within the Salsola genus [1]. Ole e 11, a pectin methylesterase from olive tree pollen display, was reported to display 70% sequence homology with Sal k 1 [8].

AIT Prescription

Detectable Sal k 1 IgE confirms genuine sensitization to S. kali, hence assisting with AIT selection [1, 9].

Exposure

The main route of exposure is through inhalation of S. kali pollen.

Compiled By

Author: Joana Vitte

Reviewer: Dr. Christian Fischer

Last reviewed:February 2022

References

Matricardi, P.M., et al., EAACI Molecular Allergology User's Guide. Pediatr Allergy Immunol, 2016. 27 Suppl 23: p. 1-250.
Carnes, J., et al., Immunochemical characterization of Russian thistle (Salsola kali) pollen extracts. Purification of the allergen Sal k 1. Allergy, 2003. 58(11): p. 1152-6.
Arilla, M.C., et al., The Russian Thistle (Salsola kali) pollen major allergen, Sal k 1, can be quantified in allergenic extracts and airborne pollen. Int Arch Allergy Immunol, 2010. 152(4): p. 319-26.
Teifoori, F., et al., Identification of the main allergen sensitizers in an Iran asthmatic population by molecular diagnosis. Allergy Asthma Clin Immunol, 2014. 10(1): p. 41.
Panzner, P., et al., A comprehensive analysis of middle-European molecular sensitization profiles to pollen allergens. Int Arch Allergy Immunol, 2014. 164(1): p. 74-82.
Al-Ahmad, M., et al., Extensive Cross-reactivity Between Salsola kali and Salsola imbricata. J Investig Allergol Clin Immunol, 2018. 28(1): p. 29-36.
Mas, S., et al., A recombinant Sal k 1 isoform as an alternative to the polymorphic allergen from Salsola kali pollen for allergy diagnosis. Int Arch Allergy Immunol, 2015. 167(2): p. 83-93.
Salamanca, G., et al., Pectin methylesterases of pollen tissue, a major allergen in olive tree. FEBS J, 2010. 277(13): p. 2729-39.
Barderas, R., et al., A pectin methylesterase as an allergenic marker for the sensitization to Russian thistle (Salsola kali) pollen. Clin Exp Allergy, 2007. 37(7): p. 1111-9.
Chebli, Y. and A. Geitmann, Cellular growth in plants requires regulation of cell wall biochemistry. Curr Opin Cell Biol, 2017. 44: p. 28-35.
Wormit, A. and B. Usadel, The Multifaceted Role of Pectin Methylesterase Inhibitors (PMEIs). Int J Mol Sci, 2018. 19(10).
IUIS/WHO. IUIS/WHO Salsola kali. 2021 2021 December 27]; Available from: http://allergen.org/search.php?allergenname=&allergensource=salsola&TaxSource=&TaxOrder=&foodallerg=all&bioname=.