Structures were fabricated.

From The Scientist:
Neither Nature nor the paper’s authors have fully explained why it took so long to retract the study. “This is a pretty old story, I don’t know why Nature took so long,” coauthor Narayana Sthanam from the University of Alabama at Birmingham (UAB) told Retraction Watch. “Nature asked us maybe two months back, do I have any comment or objection for retracting.”
Apparently, two authors did not agree to retraction.
One of the coauthors who did not agree with the retraction, former UAB researcher M. Krishna Murthy, was found “solely responsible for the fraudulent data” by the UAB investigation. More.
Note: Allegations of fraud may involve legal as well as career issues; it would be no surprise if persons were advised to reserve their defense in case of later action.
See also: Should science papers be anonymous? The problem with safeguards that don’t work is not just that they don’t work. Rather, they can work against the aims of the process.
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