Transcript What is the Evolutionary History and Function of Exendin?

What is the Evolutionary
History and Function of
Exendin?
Mary Ritke
Sandra Davis
Octavian Nicolio
Angela McKinney-Williams
Previous Observations
• GLP-1 is a ligand for the GLP-1 receptor (Methuselah)
that enhances glucose uptake in cells.
• Exendin is a protein found in the venom of the
Heloderma suspectum, a.k.a. the Gila monster
• Trp Cage is a synthetic peptide with interesting
thermodynamic properties, however Exendin has been
found to have the Trp Cage motif.
• Compared to GLP-1, Exendin binds the GLP-1
receptor more tightly and is a more effective glucose
uptake stimulator.
• What an interesting phenomenon!!!!
Heloderma suspectum
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
Our objectives are to:
• Design and test a learning module to help students
determine how to use existing data (above) to
understand the relationship between two seemingly
unrelated proteins: a venom protein and a glucose
metabolism effector. We (and our students will)
– Formulate hypotheses
– Plan experiments to further understand the
evolutionary history and function of GLP-1-like
proteins and Exendin.
• Use existing data bases to test two hypotheses regarding
the evolution of GLP-1 and Exendin.
Two Hypotheses to be tested
1. In Gila monster, Exendi n has evolved a novel function
different from GLP-1
Through gene recombination, GLP-1 or an ancestral protein
containing a GLP-1 domain and Trp protein motif have been
combined, forming a ТnewУ protein with a novel (unknown)
function, Exendin

+
GLP
domain
trp
domain
Exendin
Two Hypotheses to be tested
2. Mammalian GLP-1 has evolved from Exendin
GLP-1 evolved through the loss of the trp cage motif from Exendin
(or an exendin ancestral gene)

Exendi n
+
GLP
domai n
trp
domain
Predicted Tree Under Hypothesis 1
GLP-I
(Outgroup)
GLP-I (Human) GLP-I (Gila)?
GLP region
of Exendin
+ TrpCage
sequence
No TrpCage
sequence
Predicted Tree Under Hypothesis 2
GLP
(Outgroup)
GLP region
GLP species X of Exendin
GLP-I (Human)
- TrpCage
sequence
GLP + TrpCage
sequence
• We used BLAST to find the amino acid sequences
of GLP-I related proteins in 13 different species
–
–
–
–
–
–
–
–
–
–
–
–
–
Heloderma suspectum (Gila monster)
Hoplobatrachus rugulosus (crowned bullfrog)
Petromyzon marinus (sea lamprey)
Agkistrodon piscivorus (cottonmouth)
Gallus gallus (chicken)
Mus musculus (mouse)
Neoceratodus forsteri (Australian lungfish)
Homo sapiens (human)
Rana catesbeiana (bullfrog)
Amphiuma tridactylum (three-toed salamander)
Pan troglodytes (chimpanzee)
Ictalurus punctatus (channel catfish)
Squalus acanthias (spiny dogfish)
Method:
Neighbor Joining; Bes t Tree; tie breaking = Sy stematic
Distance: Absolute (# differenc es)
Gaps distributed proportionally
32.734
Dogfish
23.527
Lungfish
Bullfrog
16.505
22.025
9.931
15.019
8.069
CrwnBulfrg
Mouse
Human
chimp
20.052
3ToedSal
8.852
21.661
Cottnmth
20.648
Lamprey
10.0
Chicken
Catfish
GLP Gila
“Molded results vary
depending on child’s age and
level of skill”