PMID:28066334

Citation	Prasad, S, Xu, J, Zhang, Y and Wang, N (2016) SEC-Translocon Dependent Extracytoplasmic Proteins of Candidatus Liberibacter asiaticus. Front Microbiol 7:1989
Abstract	Citrus Huanglongbing (HLB) is the most destructive citrus disease worldwide. HLB is associated with three species of the phloem-limited, gram-negative, fastidious α-proteobacteria: Candidatus Liberibacter asiaticus (Las), Ca. L. americanus (Lam), and Ca. L. africanus (Laf) with Las being the most widespread species. Las has not been cultured in artificial media, which has greatly hampered our efforts to understand its virulence mechanisms. Las contains a complete Sec-translocon, which has been suggested to transport Las proteins including virulence factors into the extracytoplasmic milieu. In this study, we characterized the Sec-translocon dependent, signal peptide containing extracytoplasmic proteins of Las. A total of 166 proteins of Las-psy62 strain were predicted to contain signal peptides targeting them out of the cell cytoplasm via the Sec-translocon using LipoP, SigalP 3.0, SignalP 4.1, and Phobius. We also predicated SP containing extracytoplasmic proteins for Las-gxpsy and Las-Ishi-1, Lam, Laf, Ca. L. solanacearum (Lso), and L. crescens (Lcr). For experimental validation of the predicted extracytoplasmic proteins, Escherichia coli based alkaline phosphatase (PhoA) gene fusion assays were conducted. A total of 86 out of the 166 predicted Las proteins were experimentally validated to contain signal peptides. Additionally, Las-psy62 lepB (CLIBASIA_04190), the gene encodes signal peptidase I, was able to partially complement the amber mutant of lepB of E. coli. This work will contribute to the identification of Sec-translocon dependent effector proteins of Las, which might be involved in virulence of Las.
Links	PubMed PMC5167687 Online version:10.3389/fmicb.2016.01989
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Annotations

Gene product	Qualifier	GO Term	Evidence Code	with/from	Aspect	Extension	Notes	Status
LIBAP:C6XGA9		GO:0008236: serine-type peptidase activity	ECO:0000247:	UniProtKB:P00803	F		Experimenters conducted a sequence alignment with Liberibacter asiaticus (strain 62) with Escherichia coli (strain K-12) to confirm that serine-type pepsidase I (SPase I) is conserved. The sequence alignment was also comparing Liberibacter asiaticus (strain:gxpsy) and Liberibacter asiaticus (strain:Ishi-1). Suplementary Figure 1 shows the identity for the SPase I of the three Liberibacter asiaticus strains is 100%. The Liberibacter asiaticus SPase I protein shares 34% identity and 52% similarity with that of E. coli.	complete CACAO 12485
LIBAP:C6XGA9		GO:0008236: serine-type peptidase activity	ECO:0000315:		F		Liberibacter asiaticus lepB could partially complement the lepB mutant of E.coli. lepB is the gene that encodes Serine peptidase I. Figure 4 shows that the wild type E. coli grew at 37 degrees celcius and 42. The amber E. coli mutant grew at 37 but not 42. The lepB homolog of Liberibacter asiaticus partially restores growth of the mutant strain to result in growth at 37 and 42.	complete CACAO 12486

References

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