9.B.410. The Viral E3 CR1 (E3-CR1) Family The proteins of this family are found in a variety of eukaryotic viruses and in general, have an N-terminal TMS, probably the leader sequence that directs the nascent polypoptide chain to the membrane, and a large C-terminal TMS. The E3 region of all simian and human type viruses, classified within species of human mastadenovirus B (HAdV-B) encodes two unique highly conserved ORFs of unknown function designated E3-CR1beta and E3-CR1gamma. Lakshmi Narayan and Kajon 2020 generated a HAdV-3 mutant encoding small epitope tags at the N-termini of both E3-CR1beta and E3-CR1gamma (HAdV-3 N-tag wt) and a double knock out (HAdV-3 N-tag DKO) mutant virus that does not express either protein. Our studies show that HAdV-3 E3-CR1beta and E3-CR1gamma are type I transmembrane proteins that are produced predominantly at late times post infection, are glycosylated, co-localize at the plasma membrane of non-polarized epithelial cells, and interact with each other. At their extreme C-termini HAdV-B E3-CR1beta and E3-CR1gamma possess a conserved di-leucine motif followed by a class II PDZ domain binding motif (PBM). HAdV-3 E3-CR1beta and E3-CR1gamma are dispensable for virus growth, progeny release, spread, and plaque formation in A549 cells (Lakshmi Narayan and Kajon 2020).
References:
Engel, P., N. Pérez-Carmona, M.M. Albà, K. Robertson, P. Ghazal, and A. Angulo. (2011). Human cytomegalovirus UL7, a homologue of the SLAM-family receptor CD229, impairs cytokine production. Immunol Cell Biol 89: 753-766.
Lakshmi Narayan, P.K. and A.E. Kajon. (2020). Human mastadenovirus-B (HAdV-B)-specific E3-CR1β and E3-CR1γ glycoproteins interact with each other and localize at the plasma membrane of non-polarized airway epithelial cells. Virology 546: 67-78.
Examples:
TC#	Name	Organismal Type	Example
9.B.410.1.1	The human mastadenovirus-B (HAdV-B)-specific E3-CR1beta of 181 aas and 2 TMSs, a relatively small leader sequence at the N-terminus, and a large, very hydrophobic C-terminal TMS. The function is not defined, but it could be a redundant viroporin (Lakshmi Narayan and Kajon 2020).		E3-CR1β of human mastadenovirus-B (HAdV-B)

9.B.410.1.2	E3 CR1-gamma1 of 204 aas and 2 TMSs, N- and C-terminal.		E3-CR!γ of Simian adenovirus 25

9.B.410.1.3	The E3 22.5 kDa protein of 199 aas and 2 TMSs, N- and C-terminal.		E3 22.5 protein of Simian adenovirus E22

Examples:
TC#	Name	Organismal Type	Example
9.B.410.2.1	Membrane protein RL13 of 306 aas and 2 TMSs, and small hydrophobic peak at the N-terminus, and a large hydrophobic peak at the C-terminus.		RL13 of Human cytomegalovirus (HHV-5) (Human herpesvirus 5)

9.B.410.2.2	E3 32.1 kDa protein of 295 aas and 2 TMSs, N- and C-terminal.		E3 32.1 protein of Simian adenovirus 24

9.B.410.2.3	Rh13.1 protein of 321 aas and 2 TMSs, N- and C-terminal.		Rh13.1 of Macacine betaherpesvirus 3

9.B.410.2.4	CR1-gamma (gpE3) protein of 274 aas and 2 TMSs, N- and C-terminal.		CR1γ of Human mastadenovirus D

9.B.410.2.5	CEACAM1-like protein UL7, of 222 aas and 2 TMSs, N- and C-terminal. It plays a role in modulating the host immune response and affecting host cytokine production. It is structurally and functionally homolog of host CEACAM1, induces endothelial cell angiogenesis (Engel et al. 2011). It triggers hematopoietic progenitor cell and monocyte differentiation leading to virus reactivation (Engel et al. 2011).		UL7 of Human cytomegalovirus (strain AD169) (HHV-5) (Human herpesvirus 5)