Amt2 Permease Is Required To Induce Ammonium-Responsive Invasive Growth and Mating in Cryptococcus neoformans

Abstract

The conserved AmtB/Mep/Rh family of proteins mediate the transport of ammonium across cellular membranes in a wide range of organisms. Certain fungal members of this group are required to initiate filamentous growth. We have investigated the functions of two members of the AmtB/Mep/Rh family from the pathogenic basidiomycete Cryptococcus neoformans. Amt1 and Amt2 are low-and high-affinity ammonium permeases, respectively, and a mutant lacking both permeases is unable to grow under ammonium-limiting conditions. AMT2 is transcriptionally induced in response to nitrogen limitation, whereas AMT1 is constitutively expressed. Single and double amt mutants exhibit wild-type virulence in two models of cryptococcosis. Consistent with this, the formation of two C. neoformans virulence factors, cell wall melanin and the extracellular polysaccharide capsule, is not impaired in cells lacking either or both of the Amt1 and Amt2 permeases. Amt2 is, however, required for the initiation of invasive growth of haploid cells under low-nitrogen conditions and for the mating of wild-type cells under the same conditions. We propose that Amt2 may be a new fungal ammonium sensor and an element of the signaling cascades that govern the mating of C. neoformans in response to environmental nutritional cues.

Nitrogen Metabolite Repression of Metabolism and Virulence in the Human Fungal Pathogen Cryptococcus neoformans

“…We subsequently gained insights into this paradox by proving that along with its established role as an activator of secondary catabolic gene expression in the absence of ammonium, Gat1/ Are1 is also functional in the presence of ammonium. Like A. nidulans AreA, C. neoformans Gat1/Are1 also regulates the expression of the major ammonium assimilation enzyme-encoding gene GDH1 as well as the permease-encoding genes AMT1 and AMT2 (Christensen et al 1998;Monahan et al 2002Monahan et al , 2006Rutherford et al 2008). Since the alternative pathway of ammonium assimilation (via GLN1 and GLT1) is not significantly impaired in the gat1/are1D mutant, we speculate that the basal levels of transcription of AMT1 and AMT2 may be insufficient for ammonium uptake.…”

“…qRT-PCR was again employed, this time to analyze the transcriptional regulation of these central nitrogen metabolism genes as well as the two known ammonium permease-encoding genes AMT1 and AMT2 in both the wild-type and gat1D mutant strains ( Figure 5B) (Rutherford et al 2008). When grown in rich undefined YPD medium that contains a wide array of nitrogen sources including the generally preferred ammonium, glutamine, and glutamate, the level of expression of the major ammonium assimilation enzyme-encoding gene GDH1 as well as the permease-encoding genes AMT1 and AMT2 was significantly lower (10-20-fold) in the gat1D mutant compared to wild type (GDH1, P , 0.0001; AMT1, P ¼ 0.0086; AMT2, P ¼ 0.0308).…”

Regulation of haplid phenotypes in Ustilago maydis by ammonium transporters and components of the b mating locus.

“…For example, haploid invasive growth in response to low ammonium in S. pombe, S. cerevisiae and C. neoformans and mating response in C. neoformans are dependent on ammonium transporters (Mitsuzawa, 2006;Rutherford, Chua, et al, 2008;Rutherford, Lin, et al, 2008) The two ammonium permeases of U. maydis are involved in transporting ammonium into the cell and an additional 'sensor of ammonium' function is assigned to the high affinity ammonium transporter (Ump2). In the current study,…”

“…cerevisiae on low ammonium is dependent on these ammonium permeases, both mating and haploid invasive growth in Cryptococcus neoformans are induced by ammonium limitation and specifically require the high affinity ammonium transporter (Mitsuzawa, 2006;Rutherford, Lin, Nielsen, & Heitman, 2008).…”

Προσδιορισμός Πολυμορφισμών Του Αντιγόνου D Στον Ελληνικό Πληθυσμό

“…Παρά την κλινική σημασία τους, η λειτουργία των πρωτεϊνών Rh, παρέμεινε ασαφής, μέχρι που μελέτες, έδειξαν μικρή, αλλά σημαντική ομολογία αμινοξέων με τις πρωτεΐνες μεταφοράς αμμωνίου (Ammonium / methylammonium transporters, Amts) 170 και των ομολόγων τους περμεασών (Μethylammonium / ammonium permeases, Mep) 171 . Οι πρωτεΐνες Amt, είναι παρούσες ως μεμβρανικοί δίαυλοι στα βακτήρια (bacteria), στα αρχέα (archaea), στα φυτά (plants) και στους μύκητες (fungi) 172,173,174 , ενώ καλύτερα μελετημένες είναι στο εντεροβακτηρίδιο Escherichia coli 175,176,177 ), ένα C-τελικό άκρο το οποίο δεσμεύει την ανθρακική ανυδράση (carbonic anhydrase) και ένα μακρύ Ν-τελικό άκρο που δεσμεύει την αιμοσφαιρίνη (haemoglobin), γλυκολυτικά ένζυμα (glycolytic enzymes), την αγκυρίνη (ankyrin), την πρωτεΐνη 4.2 και την σπεκτρίνη (spectrin). Η λειτουργία του Ν-τελικού άκρου της πρωτεΐνης ζώνης 3 είναι να σταθεροποιηθεί η μεμβράνη του ερυθρού αιμοσφαιρίου στον κυτταροσκελετό (cytoskeleton).…”