Distinct transport mechanism in Candida albicans methylammonium permeases
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ORIGINAL ARTICLE
Distinct transport mechanism in Candida albicans methylammonium permeases B. Neuhäuser 1 Received: 4 March 2020 / Revised: 1 September 2020 / Accepted: 3 September 2020 # The Author(s) 2020
Abstract It is crucial for the growth and development of an organism whether ammonium is transported across its membranes in a form of NH4+ or NH3. The transport of both molecules follows different pH-dependent gradients across membranes and transport of both substrates differentially affects the internal and external pH. As a consequence, they directly influence the physiology and organism development. CaMep2 from Candida albicans shows a dual transceptor function in ammonium transport and sensing. CaMep2 senses low ammonium availability and induces filamentous growth. CaMep1, by contrast, is only active in transport, but not involved in ammonium signaling. Here, both proteins were heterologously expressed in Xenopus laevis oocytes. This study identified electrogenic NH4+ transport by CaMep1 and electroneutral NH3 transport by CaMep2, which might be a prerequisite for the induction of pseudohyphal growth. Keywords Candida albicans . Methylammonium permeases . Ammonium . Transport . Transceptor . Filamentous growth . Substrate specificity
Introduction While early experiments indicated the need of an active ammonium transport system in organismal membranes (Hackette et al. 1970), transport proteins for ammonium (this term designates to the sum of ammonium [NH4+] and ammonia [NH3]) were first identified in the 90th in the yeast Saccharomyces cerevisiae (Marini et al. 1994) and the plant Arabidopsis thaliana (AMT = AMmonium Transporter) (Ninnemann et al. 1994). In yeast, they have been identified by complementation assays showing transport of methylammonium. This determined their denomination as Meps (MEthylammonium Permeases). Upon sequence homology and functional analysis, proteins of this AMT/Mep/Rh family have been identified in a great quantity of organisms Section Editor: Martin Rühl Electronic supplementary material The online version of this article (https://doi.org/10.1007/s11557-020-01625-0) contains supplementary material, which is available to authorized users. * B. Neuhäuser [email protected] 1
Institute of Crop Science, Nutritional Crop Physiology, University of Hohenheim, Fruwirthstr. 20, 70593 Stuttgart, Germany
throughout all kingdoms of life (Ludewig et al. 2007). All these ammonium transporter proteins share a high sequence homology and a common protein structure with 11 transmembrane helices forming a central pore (Mayer et al. 2006). Three subunits build a functional trimer which is regulated by the interaction of the subunits (Yuan et al. 2007; Loqué et al. 2007; Neuhäuser et al. 2007). Within the substrate transporting pore, the homology between the transporters is especially pronounced (Neuhäuser et al. 2009, 2014). Therefore, it is surprising that different transport mechanisms have been proposed for different protein subfamilies or transporters from different organism
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