Table 1.
Rickettsial proteins with known or predicted roles during infection. Summarized details of key rickettsial proteins discussed in this review. The presence of a protein in a specific rickettsial group is defined by a full or partial homolog found in the genome of at least one species. Asterisks (*) denote studies that directly characterized the protein in the native Rickettsia species by studying a mutant strain of rickettsia. SFG, spotted fever group; TG, typhus group; TRG, transitional group; AG, ancestral group.
| Rickettsial Protein | Known host protein interactions | Function | Present | References | |
|---|---|---|---|---|---|
| Secreted | TlyA | Unknown | Predicted hemolysin with possible role in vacuole escape and/or host cell lysis |
SFG, TG, TRG, AG | R. prowazekii (Whitworth et al. 2005) |
| TlyC | Unknown | Predicted hemolysin with possible role in vacuole escape and/or host cell lysis |
SFG, TG, TRG, AG | R. prowazekii (Whitworth et al. 2005) | |
| Pat1 | Unknown | Phospholipase with possible role in vacuole escape and/or host cell lysis |
SFG, TG, TRG, AG | R. rickettsii (Walker et al. 1983; Silverman et al. 1992), R. typhi (Rahman et al. 2010, 2013) | |
| Pat2 | Unknown | Phospholipase with possible role in vacuole escape and/or host cell lysis |
SFG, TG, TRG, AG | R. rickettsii (Walker et al. 1983; Silverman et al. 1992),R. typhi (Rahman et al. 2010, 2013) | |
| PLD | Unknown | Predicted phospholipase with possible role in vacuole escape and/or host cell lysis |
SFG, TG, TRG, AG | R. prowazekii (Whitworth et al. 2005, Driskell et al. 2009*) | |
| Sca4 | Vinculin | Disrupts interaction between vinculin and α-catenin promote cell-to-cell spread |
SFG, TG, TRG, AG | R. rickettsii (Park et al. 2011), R. parkeri (Lamason et al. 2016*) | |
| Risk1 | Beclin-1 | Phosphatidylinositol 3-kinase activity promotes host cell colonization |
SFG, TG, TRG, AG | R. typhi (Voss et al. 2020) | |
| RalF | Arf6 | Guanine nucleotide exchange factor of Arf6 that promotes invasion | TG, TRG, AG | R. typhi (Rennoll-Bankert et al. 2015, 2016) | |
| RARP-2 | Unknown | Cysteine protease that contributes to trans-Golgi fragmentation |
SFG, TG, TRG, AG | R. rickettsii (Lehman et al. 2018; Aistleitner et al. 2020) | |
| Surface or membrane | Tlc1 | Unknown | ATP/ADP symporter that imports ATP from host cells |
SFG, TG, TRG, AG | R. prowazekii (Winkler 1976; Audia and Winkler 2006; Krause, Winkler and Wood 1985) |
| OmpA | α2β1 integrin | Rickettsial surface protein involved in invasion |
SFG, TRG, AG | R. conorii (Hillman, Baktash and Martinez 2013) | |
| OmpB | Ku70 | Rickettsial surface protein involved in invasion and autophagy avoidance |
SFG, TG, TRG, AG | R. conorii (Martinez et al. 2005), R. parkeri (Engström et al. 2019*) | |
| PKMT1/2 | Unknown | Lysine methylation of rickettsial surface proteins to avoid autophagy |
SFG, TG, TRG, AG | R. parkeri (Engström et al. 2020*), R. prowazekii (Abeykoon et al. 2012, 2014, 2016), R. typhi (Abeykoon et al. 2014, 2016) | |
| RickA | Arp2/3 | Mimics WASP to activate Arp2/3 to drive actin-based motility |
SFG, TRG, AG | R. conorii (Gouin et al. 2004), R. rickettsii (Jeng et al. 2004), R. parkeri (Reed et al.2014*) | |
| Sca2 | Actin, profilin | Formin-like activity that directly nucleates actin to promote motility |
SFG, TG, TRG, AG | R. rickettsii (Kleba et al. 2010*), R. parkeri (Haglund et al. 2010, Reed et al. 2014*), R. conorii (Madasu et al. 2013) |