D7r1 Review Notes - Anopheles gambiae

Gene Overview

D7r1 (D7-related 1) is a short-form salivary protein from Anopheles gambiae (African malaria mosquito). It belongs to the PBP/GOBP (Pheromone/Odorant-Binding Protein) family.

Key Literature Findings

Core Function

D7r1 "modulates blood feeding of female mosquitoes on vertebrate species by binding and sequestering different mediators involved in the host response" [PMID:16301315, UniProt].

Specifically:
- Binds serotonin and histamine with high affinity PMID:16301315
- Increases blood clotting time PMID:16301315
- Acts as a "kratagonist" - sequesters host signaling molecules rather than blocking receptors

Mechanism - Kratagonism

D7 proteins show a unique type of agonist inhibition called "kratagonism" - they bind biogenic amines (serotonin, histamine, norepinephrine, epinephrine) with high affinity, effectively sequestering them and preventing their action on host tissues.

From PMID:17928288 (D7r4 crystal structure):

"The D7r proteins bind the biogenic amines serotonin, norepinephrine, and histamine with high affinity"
"The D7 fold consists of an arrangement of eight alpha-helices stabilized by three disulfide bonds"

Tissue Expression

Stoichiometry

D7 proteins bind ligands in a 1:1 stoichiometric ratio, which explains why they are among the most abundant components of mosquito salivary glands - they need to be at equimolar concentrations with host mediators (1-10 μM for histamine/serotonin).

D7 Family in A. gambiae

GO Annotation Assessment

Current Annotations

  1. GO:0090729 (toxin activity) - SPKW via GO_REF:0000043

  2. UniProt keywords: "Blood coagulation cascade inhibiting toxin", "Hemostasis impairing toxin"

  3. GO:0005549 (odorant binding) - InterPro via GO_REF:0000002

  4. Based on PBP/GOBP family membership

  5. GO:0005576 (extracellular region) - UniProt subcellular location via GO_REF:0000044

  6. Protein is secreted into saliva

  7. GO:0035821 (modulation of process of another organism) - GOC via GO_REF:0000108

  8. Inferred from toxin activity annotation

Critical Assessment: Is "toxin activity" appropriate?

GO:0090729 definition: "Interacting selectively with one or more biological molecules in another (target) organism, initiating pathogenesis (leading to an abnormal, generally detrimental state) in the target organism."

Assessment: D7r1 does NOT meet this definition because:
1. It does NOT initiate pathogenesis - it transiently modulates host physiology
2. It does NOT cause disease or tissue damage
3. Its effect is reversible and temporary (duration of feeding)
4. The host returns to normal state after feeding
5. The function evolved to facilitate feeding, not to harm the host

However: D7r1 DOES:
- Bind serotonin (GO:0051378)
- Bind histamine (GO:0051381)
- Negatively regulate hemostasis in the host (GO:1900047)
- Modulate processes in another organism (GO:0035821 - already annotated!)

  1. GO:0090729 (toxin activity): MARK AS OVER-ANNOTATED
  2. The term implies pathogenesis, which doesn't occur

  3. More accurate: This is anti-hemostatic activity, not toxin activity

  4. GO:0005549 (odorant binding): MODIFY or KEEP_AS_NON_CORE

  5. Based on structural family membership, but D7r1 doesn't actually function in olfaction

  6. It binds biogenic amines as ligands, not odorants

  7. GO:0005576 (extracellular region): ACCEPT

  8. Protein is secreted, this is accurate

  9. GO:0035821 (modulation of process of another organism): ACCEPT

  10. Accurately describes the function

Proposed New Annotations

  1. GO:0051378 (serotonin binding) - MF

  2. Evidence: PMID:16301315 demonstrates serotonin binding

  3. GO:0051381 (histamine binding) - MF

  4. Evidence: PMID:16301315 demonstrates histamine binding

  5. GO:1900047 (negative regulation of hemostasis) - BP

  6. Evidence: D7r1 increases clotting time PMID:16301315

References

Sources