9.B.306.  The Putative Calcium Binding Protein with Similarity to the C-termini of Anoctamins (CBP) Family

This family usually consist of short protein of about 140 - 160 aas with 5 TMSs. The last 4 TMSs of these proteins resemble the C-terminal 4 TMSs in the Anoctamins of subfamily 1.A.17.5. The last 4 TMSs of both (sub)families occur in a 2 + 2 TMS arrangement, and in the annoctamins, they comprise a Ca2+ binding site that controls channel activity.  The channel immediately precedes the calcium binding domain. Therefore, the small proteins of the CBP family may be calcium binding proteins.

One of these proteins, 9.B.306.1.1, gave a BLAST score of e-6 with 1.A.17.5.6 (25% identity) in the Anoctamin superfamily, again with the last 4 TMSs of both proteins aligning. Using the complexity filter and/or the composition filter did not decrease the BLAST score as it remained 10-6. This supports the conclusion that the small proteins of the 9.B.306 family are calcium binding proteins.

One small protein (9.B.306.1.7) of 65 aas, has 2 TMSs that correspond to the last two TMSs in the other family members.  It is not known if the former protein is a fragment or a full length protein with just half as many TMSs as usual. Additionally, the 4 or 5 TMSs of the CBP family proteins may be distantly related to rhomboid proteases (i.e., TC# 9.B.104.1.12) and certain membrane anchored dehydrogenases (i.e., TC# 5.B.2.3.3).

This family belongs to the .


TC#NameOrganismal TypeExample

Uncharacterized protein of 152 aas and 5 TMSs.

UP of Anaerolineaceae bacterium 4572_5.2 (marine sediment metagenome)


Uncharacterized protein of 146 aas and 5 TMSs

UP of Chloroflexi bacterium


Uncharacterized class A beta-lactamase-related serine hydrolase with 514 aas and 6 TMSs and a beta-lactamase domain.

β-Lactamse of Anaerolineales bacterium


Uncharacterized protein of 144 aas and 5 TMSs

UP of Trichococcus ilyis


Uncharacterized protein of 149 aas and 5 TMSs.

UP of Melioribacter roseus


Uncharacterized protein of 147 aas and 5 TMSs.

UP of Candidatus Thorarchaeota archaeon SMTZ-45 (sediment metagenome)


Uncharacterized protein of 65 aas and 2 TMSs.  These two TMSs correspond to the last two TMSs of the other homologues.  It could be a real protein, or it could be a fragment.

UP of Mesotoga infera


Uncharacterized protein of 87 aas and 2 TMSs.  This protein is homologous to other members of the UPSA family with the greatest similarity to the 2 TMS homologue with TC # 9.B.306.1.7 (68% identity).

UP of Chloroflexi bacterium RBG_13_51_36 (sediment metagenome)


Uncharacterized protein of 156 aas and 5 TMSs

UP of Candidatus Atribacteria bacterium CG2_30_33_13 (groundwater metagenome)


TC#NameOrganismal TypeExample

Uncharacterized protein of 140 aas and 5 TMSs

UP of Phycicoccus sp. Soil748


Uncharacterized protein of 148 aas and 5 TMSs

UP of Longilinea arvoryzae


Uncharacterized protein of 143 aas and 5 TMSs

UP of Mesotoga infera


Uncharacterized protein of 152 aas and 5 TMSs

UP of Theionarchaea archaeon DG-70


Uncharacterized protein of 155 aas and 5 TMSs

UP of Arthrobacter sp. TB 26


TC#NameOrganismal TypeExample

Uncharacterized protein of 161 aas and 5 TMSs.

UP of Thermoplasmatales archaeon SM1-50 (sediment metagenome)


Uncharacterized protein of 169 aas and 5 TMSs.

uP of Candidatus Bathyarchaeota archaeon RBG_16_57_9 (subsurface metagenome)


TC#NameOrganismal TypeExample

Putative membrane-bound PQQ-dependent dehydrogenase of the glucose/quinate/shikimate family.  The N-terminal TMSs may be homologous to other members of the CBP family, but this has not been established. 

PQQ-dependent dehydrogenase of Serratia sp. M24T3


Pyrroloquinoline quinone-dependent dehydrogenase of 796 aas and 5 N-terminal TMSs that may be homologous to the 5 TMSs of the CBP family.

PQQ DH of E. coli