Liberibacter asiaticus (Ca.
L. asiaticus) is a Gram-negative Alphaproteobacterium
. It is closely associated with Huanglongbing (HLB, also called citrus greening), one of the most severe worldwide diseases of citrus. The ranking Candidatus
is assigned to this bacterium because it cannot be maintained in bacterial culture. In nature, the bacterium is transmitted among citrus plants by the piercing-sucking insect, Asian citrus psyllid (Diaphorina citri Kuwayama
) and it resides in the phloem tissue of citrus plants. Infected plants gradually develop symptoms such as yellow leaves, premature defoliation and aborted fruits, followed by the eventual death of the entire plants 
. It is hypothesized that Ca.
L. asiaticus infection could induce over-accumulation of callose in plant plasmodesmata pore units and sieve pores, inhibiting phloem transport and contributing to HLB symptoms 
Ever since HLB was described, efforts have been devoted to understanding the plant response to the infection 
, and to diagnosing 
and controlling the disease 
. However, a fundamental understanding of the HLB mechanism or an ultimate way to treat the disease has yet to manifest. This lack of accomplishment is due in part to the limited success in culturing the bacterium 
, which makes carrying out experiments directly on Ca.
L. asiaticus a challenge.
In 2009, the complete genome sequence of Ca.
L. asiaticus was obtained 
and verified 
, allowing researchers to study Ca.
L. asiaticus proteins in vitro
or through heterologous expression. Through such experiments, the function of a hypothetical ADP/ATP translocase has been verified 
and a moderate inhibitor of the predicted secA
gene product has been identified 
. These findings demonstrate the possibility of understanding and controlling HLB at the molecular level. Given the genome sequence, computational analysis combined with manual curation can stimulate such research by predicting the structure and function of Ca.
L. asiaticus proteins, identifying potential virulence factors and selecting drug targets to specifically inhibit the bacterium.
L. asiaticus genome is highly reduced relative to other bacteria in the order Rhizobiales
, likely related to its intracellular lifestyle 
. Gene prediction and annotation pipeline from National Center for Biotechnology Information (NCBI) 
and the Rapid Annotations using Subsystems Technology (RAST) server 
have predicted 1,233 protein-coding genes in the entire genome. This relatively small genome size allows careful analysis of all the Ca.
L. asiaticus proteins in silico
. Protein sequence analysis relies heavily on detection of homologs 
. The 3D structures of homologous proteins provide templates for structure modeling, and the function annotations of close homologs (orthologs) can be transferred in most cases to the protein of interest. Meanwhile, in the absence of confident homologs, other evidence can provide hints to protein function, including the presence of certain functional motifs, the predicted 3D structure, the genomic context, the phylogenetic distribution, the known physical interaction, functional association between proteins and detection of local sequence features such as signal peptides (SPs) and transmembrane helices (TMHs) 
Here we report computational analysis followed by partial manual curation of the Ca.
L. asiaticus proteome. Information from various databases was gathered for each protein and essential sequence features, such as SPs and TMHs, were predicted. Moreover, the evolutionarily related proteins, protein families, protein structures and domains were detected for each Ca.
L. asiaticus gene product by multiple procedures. Results from these bioinformatics analyses were compiled as a website at http://prodata.swmed.edu/liberibacter_asiaticus/
. On the basis of this information, in-depth manual analysis can be performed to predict subcellular localization, validate function predictions, generate structural models, analyze domain architectures and, most importantly, identify potential effectors of this pathogen and targets for treating HLB. To illustrate the potential applications of the database, we predicted the 3D structure and function of each Ca.
L. asiaticus protein (summarized in an additional website at http://prodata.swmed.edu/liberibacter_asiaticus/curated/
). Specifically, we revealed several potential virulence factors that may be helpful to understand and control HLB from analyzing duplicated proteins and the proteins whose closest homologs are from phylogenetically distant species.