**1. Introduction**

*Tuberculosis* (TB) is primarily caused by *Mycobacterium tuberculosis* (*M. tuberculosis*) and considered to be an airborne disease that spreads through sneezing (air borne fine droplets), direct contact, and sharing personal daily use items [1]. Many attempts have been made to control and cure TB and its related critical consequences. However, several factors complicate the treatment strategy, such as the emergence of multidrug resistance against established drugs due to regular mutations, patients having poor access to drugs, long-term therapy, poor

**Citation:** Beg, M.A.; Shivangi; Afzal, O.; Akhtar, M.S.; Altamimi, A.S.A.; Hussain, A.; Imam, M.A.; Ahmad, M.N.; Chopra, S.; Athar, F. Potential Efficacy of *β*-Amyrin Targeting Mycobacterial Universal Stress Protein by In Vitro and In Silico Approach. *Molecules* **2022**, *27*, 4581. https://doi.org/10.3390/ molecules27144581

Academic Editor: Anna Maria Almerico

Received: 29 May 2022 Accepted: 14 July 2022 Published: 18 July 2022

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patient adherence, and severe dose-dependent side effects [2]. These factors have resulted in progressive growth of latent and active TB cases annually, as reported by the World Health Organization in 2021 (WHO, 2021). The WHO estimated that there were approximately 9.9 million TB cases in 2020, wherein there were about 1.3 million with HIV-negative and 0.214 million with HIV-positive cases [3–5]. Notably, the disease affects patients of all ages, the elderly, and the immunocompromised [6,7]. Circulating TB strains are now resistant to a variety of therapeutic combinations and because the discovery of novel drugs takes time, an alternative approach to provide adjuvants that can boost antibiotics potency is to be considered. It was reported that bacterial susceptibility to antibiotics increases with the co-administration of some natural products [8–10].

In this study, we investigated three medicinal plants, *Achyranthes aspera* (*A. aspera*), *Calotropis gigantea* (*C. gigantea*) and *Calotropis procera* (*C. procera*), for their potential therapeutic intervention in TB. *A. aspera* is a widely known weed in many southeast Asian countries. The plant has been used as a folk medicine in Australia, Kenya, and India, since ancient times. In India, it has been used to treat dropsy, hydrophobia, snake bites, ophthalmic, and cutaneous diseases [11–13]. As a part of the Amaranthaceous family, it is also used to treat asthma, kidney stones, skin diseases, and epilepsy [14]. Previous studies have also reported it as being antidepressant, antioxidant, anxiolytic, anticonvulsant, antihyperglycemic, antiallergenic, anti-obese, hypolipidemic, and hepatoprotective [15–19].

*Calotropis* is a common wasteland weed, commonly known as milkweed or swallowwort [20]. It is a member of the Asclepiadaceae family (Milkweeds), which has almost 2000 species globally and has a common place in the tropics, and subtropics, but is rare in cold climates [21]. Traditionally, *Calotropis* has been used to cure common ailments, such as cold, asthma, vomiting, and diarrhea. The dried whole plant is a tonic, expectorant, depurative, and anthelmintic, according to Ayurveda. Asthma, bronchitis, and dyspepsia are treated with the powdered root. Paralysis, arthralgia, swellings, and intermittent fevers can be treated with the leaves and its flowers, due to its bitter, digestive, astringent, stomachic, anthelmintic, and tonic properties. Moreover, it is a well-known homoeopathic remedy [22].

*C. procera* is an Asclepiadaceae shrub native to Egypt. It has purgative, antibacterial, anthelmintic, anticoagulant, antipyretic, anti-inflammatory, analgesic, and neuromuscular blocking properties [23–27]. The plant's extract has physiological effects on cardiac, soft, and skeletal muscular tissues. In traditional medicine, the genus *Calotropis* is used to treat leprosy, ulcers, tumors, liver, and piles problems. It also has potential anticancer effects [28]. The key phytoconstituents are practically found in every *Calotropis* species. However, the relative distribution in individual plants can vary depending upon environmental conditions [29–32].

The increased incidence of TB cases and drug resistant strains prompted us to identify novel drug targets and natural therapeutics with lesser toxicity. Considering the broad spectrum of biological properties of *A. aspera*, *C. gigantea* and *C. procera* medicinal plants, we investigated the effect of their phytoconstituents on mycobacterial proteins and their survival.
