Type II NADH: menaquinone oxidoreductase of Mycobacterium tuberculosis.

Mycobacterium tuberculosis (Mtb) remains the deadliest bacterial pathogen worldwide, causing an estimated 1.7 million deaths in 2004 among an infected population of approximately 2 billion people, according to the World Health Organization (WHO). Therapeutic options are limited to a few drugs that are becoming increasingly ineffective. Multidrug-resistant (MDR) Mtb strains are prevalent globally, fueled by inadequate patient compliance of drug intake. Recently, a high incidence of extensively drug-resistant (XDR) strains resistant to all currently used drugs was reported among patients with the human immunodeficiency virus (HIV) in KwaZulu Natal, South Africa [1]. The high mortality rate and short survival time of patients with XDR Mtb was especially alarming. The emergence of XDR mycobacteria emphasizes the urgent need for the identification of novel targets and development of new drugs. New potential drug targets exist in the Mtb respiratory chain. Certain classes of drugs have long been shown to exert significant tuberculocidal activity, such as the phenothiazines [2, 3]. Phenothiazines inhibit one of the key enzymes of the respiratory chain; type II NADH:menaquinone oxidoreductase or NDH-2 [4]. The effectiveness of this class of drugs against Mtb justifies further research into the respiratory chain, with the aim of elucidating its physiologic roles in in vitro and in vivo survival, and discovering new (sub)classes of drugs that can safely serve as inhibitors for clinical use. In this chapter, we critically review the recent advances in this field, with particular emphasis on NDH-2, and underscore the kinds of research further needed for drug development.