Complement C6 is a plasma protein involved in assembly of the membrane attack complex, a multiprotein structure capable of creating a pore in a target cell membrane. It participates downstream of complement C5 activation, when the larger fragment C5b supplies an assembly platform. The intact circulating protein and the assembled pore are different molecular objects.[ref]
Structure of complement C6 suggests a mechanism for initiation and unidirectional, sequential assembly of membrane attack complex (MAC) by Alexander E. Aleshin and others. Introduction: terminal-complement components and assembly sequence
A 2012 study determined a full-length complement C6 crystal structure and compared it with related pore-forming proteins. The authors used those structural relationships to propose a mechanism for sequential assembly. The measured structure and the proposed sequence of conformational changes are different kinds of result; a structure of isolated complement C6 is not a direct recording of a complete pore assembling.[ref]
Structure of complement C6 suggests a mechanism for initiation and unidirectional, sequential assembly of membrane attack complex (MAC) by Alexander E. Aleshin and others. Introduction and Results, Overall Structure of C6: crystal structure and proposed mechanism
For an original stoichiometric bound, assume a model with one complement C6 per C5b-containing assembly. Nine available C5b molecules but only six available complement C6 molecules allow at most six such assemblies. This count does not guarantee six finished pores: later components, binding competence and assembly conditions also matter.[ref]
Structure of complement C6 suggests a mechanism for initiation and unidirectional, sequential assembly of membrane attack complex (MAC) by Alexander E. Aleshin and others. Introduction: one copy of C6 in the mature complex
A complementary functional readout is hemolysis. The 1965 isolation study of complement C5 found that its reported lytic function depended on complement C6. Combining component-dependence assays with structural evidence connects a molecular participant to a biological effect without equating protein amount with completed pore number.[ref]
New to topics? Read the docs here!