How to keep a node at the centre of circle layout in cytoscape.js? - cytoscape.js

Question

I am trying to show metabolite-protein interaction using cytoscape.min.js. I am using the circle layout to view the network.
I have two types of node in the network,"prot" and "met". For the better visualization, I want to create a circular layout with the node "met" at the center. In this case, I want to keep the metabolite (here node 'a') at the center of the circle. How to do the same ?
Thanks,
Santosh
My script for cytoscape.min.js is as follows:
<script>
var cy = cytoscape({
container: document.getElementById('cy'),
elements: [
// nodes
{ data: { id: 'a', type: "met" } },
{ data: { id: 'b', type: "prot" } },
{ data: { id: 'c', type: "prot" } },
{ data: { id: 'd', type: "prot" } },
{ data: { id: 'e', type: "prot" } },
{ data: { id: 'f', type: "prot" } },
// edges
{
data: {
id: 'ab',
source: 'a',
target: 'b'
}
},
{
data: {
id: 'ae',
source: 'a',
target: 'e'
}
},
{
data: {
id: 'cd',
source: 'c',
target: 'd'
}
},
{
data: {
id: 'ef',
source: 'e',
target: 'f'
}
},
{
data: {
id: 'ac',
source: 'a',
target: 'c'
}
},
{
data: {
id: 'be',
source: 'b',
target: 'e'
}
}
],
style: [
{
selector: 'node[type="prot"]',
style: {
'shape': 'circle',
'background-color': 'red',
label: 'data(id)'
}
},
{
selector: 'node[type="met"]',
style: {
'shape': 'square',
'background-color': 'blue',
label: 'data(id)'
}
}]
});
cy.layout({
name: 'circle',
animate: true
}).run();
</script>