Expression of a Chitinase Gene and Lysis of the Host Cell Wall during Chlorella Virus CVK2 Infection

Abstract

A chitinase gene (vChti-1) encoded by the Chlorella virus CVK2 was cloned and characterized. The vChti-1 open reading frame consisted of 2508 bp corresponding to 836 amino acid residues. The predicted amino acid sequence contained two sets of a family 18 catalytic domain that is responsible for chitinase activity. Northern blot analysis revealed that the vChti-1 gene was expressed in virus-infected Chlorella cells late in infection, when a single transcript of about 2.5 kb appeared at 120 min postinfection. This result was confirmed by Western blotting with a specific anti-vChti-1 protein antibody; a protein of about 94 kDa was detected specifically beginning at 240 min postinfection and was present until cell lysis. The protein was not incorporated into viral particles but remained in the medium after cell lysis. The vChti-1 protein produced in virus-infected cells showed chitinase activity on zymogram assays.

Unusual Life Style of Giant Chlorella Viruses

“…These enzymes include two chitinases, a chitosanase, a β-1,3-glucanase, and another enzyme that partially degrades NC64A cell walls. Recombinant proteins produced from these five genes have the expected enzyme activities (71,72,(185)(186)(187)(188)234). Enzymes packaged in the virion and involved in virus infection are expected to be expressed late in the infection cycle.…”

The deduced role of a chitinase containing two nonsynergistic catalytic domains

“…Chitinases with two GH18 domains have been discovered in viruses, archaea, bacteria and insects (Hiramatsu et al, 1999;Tanaka et al, 2001;Howard et al, 2004;Arakane & Muthukrishnan, 2010;Itoh et al, 2016). In some of these chitinases, the two catalytic domains work synergistically because the two domains in combination exhibit a significantly higher activity than the sum of their individual activities.…”

Overexpression, purification, and characterization of Paenibacillus cell surface-expressed chitinase ChiW with two catalytic domains

“…2-40 (Sd-ChiB), 24) and vChti-1 chitinase of the Chlorella virus CVK2 (vChti-1). 25) Although no typical chitin binding domains were annotated in the sequence of ChiW (Figs. 1 and 2), the other chitinases with two catalytic domains have CBMs for chitin binding (Fig.…”

“…1) have been identified in a wide range of organisms, i.e. hyperthermophilic archae, 22,23) a marine bacterium, 24) and a Chlorella virus, 25) they differ in the composition of domains and the geometry of domain combinations (Fig. 1).…”