AustralianSuper has taken one of the largest steps to date into the growing gap left by Australia's big four banks, with investment manager MaxCap arranging a $360 million deal for the local super fund to develop Brisbane's new home for mining giant Rio Tinto.

AustralianSuper is the sole debt funder of the Midtown Centre in the Brisbane CBD, which will develop 45,000 square metres of office space by joining two existing towers into a single 26-storey tower, under a Fender Katsalidis design that creates a new role for older buildings with floorplates too small to meet modern demands.