US/UK - CalPERS and The Pensions Regulator (TPR) have lost senior staff.
Johnson said: "This new position is the next step on my career ladder. It presents a tremendous opportunity to apply my passion in a private sector environment and an opportunity to work for a company that shares the vision for high standards of corporate governance."
CalPERS said Johnson would also step down from his chairmanship of the Council of Institutional Investors Board of Directors.
Until a replacement is found, Eric Baggesen, who joined at the end of May as senior investment officer, public equities, has assumed the role.
Johnson's departure is the latest in a series of senior exits from CalPERS this year including CIO Russell Read, CEO Fred Buenrostro and SIO Christianna Wood.
Martine Trouard-Riolle, head of corporate risk management, TPR, has lost her position as a result of a management restructure after three years at the body.
June Mulroy, business delivery director, credited Trouard-Riolle with enhancing the clearance process and successfully leading a number of anti-avoidance cases as a critical part of the organisation's risk-based approach to regulation.
Trouard-Riolle's responsibilities have been taken over by Ian Cordwell until a new management structure has been established.
A suite of liability driven investment (LDI) indices has been launched by STOXX and RiskFirst to aid trustees and consultants select, monitor and challenge managers.
British Airways and the trustees of one of its pension schemes are set to argue over the purpose of a pension scheme, leading to an impactful judgment for DB pensions. James Phillips explores the issue
Bank of England governor Mark Carney has said there is still a lot of data to consider before the Monetary Policy Committee (MPC) can decide when to next hike interest rates.
Savers are not squandering their tax-free lump sums under Freedom and Choice but are taking a more cautious approach to retirement, according to Prudential research.