= Complement C7
<Complement C7> is a <protein> of the terminal <complement system>, recruited after <C5b> has associated with <complement C6>. It helps form the membrane-associated precursor to the <membrane attack complex>. It is one component of an ordered assembly, rather than a complete pore by itself.<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 assembly sequence]{ref}
A 2016 <cryo-electron microscopy> study placed <complement C7> between the early precursor and <complement C8>. Contacts on different parts of <complement C7> connected it with both neighbors, explaining how one component can help propagate assembly. Its presence was also checked by <mass spectrometry> and functional evidence.<Structural basis of complement membrane attack complex formation by Marina Serna and others>[Results: Molecular architecture of the MAC; Auxiliary domains and MAC assembly]{ref}
An original supply model makes the sequential dependency tangible. Suppose eight competent early precursors are available but only five <complement C7> molecules, and each completed intermediate requires one. At most five such intermediates can form. Supplying more <complement C9> would not remove the shortage at this earlier step. The count is an upper bound under the stipulated model, not a predicted yield of functioning pores.
A useful functional comparison would reconstitute a defined set of components with and without <complement C7>, measuring both assembled material and membrane leakage. Detecting the protein, detecting a complex and detecting leakage answer different questions. A failed leakage assay alone would not identify which assembly step failed.
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